Monsters spawn on leaves and glass

Versions: 1.14.0.1 - 1.14.0.6 

Platform: MCPE Samsung Galaxy S9+

Worlds: Local Worlds, both Creative and Survival.

Issue: Mobs spawn on any blocks, including Transparent blocks like Leaves and Glass.

This causes hostile mobs to constantly be spawning on the tops of trees, making areas that were originally safe, now extremely dangerous.

I forgot to mention that they spawn in trees. We've gotten a number of reports of them spawning in well-lit areas, but I haven't been able to reproduce that problem. I think what may be happening is that they spawn in the trees and drop to the ground. If you don't see them drop and just discover them when you turn, it would only be natural to assume they spawned on the ground where it's lit up.

Quick comment to update mobs still spawning on leaves and glass in beta 1.14.1.2

they are spawning on leaves for me in 1.14. I must add that it is not a common occurrence. For me its maybe 1 out of every hundred spawns

This bug is due to changes to the spawning algorithm in 1.14 to stop surface spawns from being passed downwards by bottom slabs and non-solid blocks. When searching for a surface spawn, the algorithm now terminates early and returns false (instead of continuing downards). However the return value is not checked, causing the game to try to spawn mobs at the location the search terminated.

The Fix: Check the return value and don't try to spawn surface mob if the search function terminated early.

Developers: A code analyzer on the TechRock Discord discovered what they think is the cause of this problem, using reverse engineering. They posted their explanation in the comment above. It was then realized that the same bug would likely cause surface spawns to be converted to cave spawns, so I verified that it did and created MCPE-58670 to report it. If the analysis is correct, the fix should be checked to ensure that it fixes both bugs.

Yeah. My creeper farms roof was perfectly fine in leaves and after 1.14 it now spawns mobs

Added a demo world. It's a flat world where the surface is half glass, half leaves out to a distance of 128 blocks. Just enable mob spawning and watch them spawn.

Can confirm this also affects transparent block such as glass, chests, bottom slabs. Basically anything seems spawnable now.

Can confirm hostile mob spawning on glass and bedrock on xbox1

Please remember that the bug tracker is not a discussion forum. Comments are intended for providing additional information to help the developers find the bug, such as additional symptoms and platforms affected or ways to work around the issues. Other comments tend to dilute and scatter this information and are subject to being removed.

A fix for this issue was intended to be included in the 1.14.0 release, but was apparently withdrawn at the last minute. I don't know why, but the most likely reason is that the test team discovered in the last stages of testing that it had unintended side effects on some other aspect of game mechanics, and there wasn't time to fix the problem before the release had to be sent out to the app stores.

Mojang realizes this issue is going to affect vast numbers of players, and getting a corrected fix is a priority. Of course, I can't predict when it will come since I don't know the details of what went wrong, but I can assure you that nobody has been ignoring this bug report (even though it only had 10 votes prior to the release).

Mobs also spawn on other non-full blocks such as stairs. I had a creeper spawn on top of a wall where the top block was quartz stairs.

I would like to confirm that mobs are not spawning on bottom half slabs in 1.14.0

@unknown: Mobs shouldn't spawn on bottom slabs, so did you mean you're confirming that it works correctly?

This is happening to me as well (1.14 Win10 PC). They also spawning in well lit areas. I had a creeper spawn in the middle of a 7x7 corral full of cows; torch on every corner and middle side-posts. The only way in was a carpet on a post.

Mobs are confirmed to be spawning on bottom 1/2 slabs. The top of my mob farm is only bottom half slabs and continuously has spawns. Again, not in single player worlds. Only Realms. Single player downloads of the same world seem fine.

I believe your reports of mobs spawning in well-lit areas and on bottom slabs, but I think these might be misinterpretations. When I specifically test for these spawns under conditions where no other types of spawns are possible, nothing spawns. But I have a possible explanation for the contradiction.

The actual bug involved has to do with how the game decides where to spawn a mob. Under some circumstances, it finds a surface block when it is trying to spawn a cave mob. Because it checked for light in the dark cave, it didn't fail due to light levels. But when it goes to actually do the spawn, it does so on the surface block instead. Since it never tested spawn conditions for the surface block, no spawn-blocking conditions that may be present at the surface matter, including light levels, block type, or density cap.

Can confirm leaves and glass.  They are also now spawning on carpet (only spiders), on the block underneath scaffolding, on buttons, and on path blocks.

this ruins SO MANY farms for us! Please fix soon

Just uploaded foxes spawning on stone blocks in a roofed cave ravine and a pillager patrol inside leaves.

Affected XB1X 1.14 release version. Hostile spawn on leaves - top of the trees.

Since the update yesterday mobs are spawning all over trees and grass.
Effected both switch console and pc win 10 minecraft.
Mobs also spawning within any distance of the player. I had a creeper spawn 2 blocks away and 5 zombies within 10 blocks. On 2 seperate occassions at different log in times.

Can confirm hostile mobs spawning at night on tree tops on our realm since the 1.14 update

Auldrick: Yes, I was confirming that the expected behavior occurs: mobs do not spawn on bottom slabs. I just wanted to clarify, because other people were claiming otherwise, but I tested in a superflat world of all bottom slabs. No mobs spawned.

Can confirm that ALL mobs are spawning in unusual blocks when light reaches a low enough level. I even got myself bombed by a creeper falling from a tree.

Reading through the comments it is hard to imagine a bug that is worse than mobs spawning in previously safe areas. I will lose litterally dozens of hours of work if i log in to the server i play on. A 20 chunk pixel art base that is spawn proofed with slabs is now a mob farm.

I understand that QA was testing and found out that it broke some undisclosed feature and the patch was removed at the last minute. The bug that was left in is worse than any other active bugs due to the creepers and enderman. They both destroy builds that take hundreds of hours to put together.

" We've gotten a number of reports of them spawning in well-lit areas, but I haven't been able to reproduce that problem."

I'm not sure if you are count pillager raid parties in that statement but pillager raid parties are 100% spawning in well-lit areas.

No, that statement wasn't meant to apply to raid spawns. They have entirely separate rules for spawning, that are not the subject of this report.

In response to Auldrick: It would be extremely helpful for everyone (developers, beta testers, and players) if there was an official reference to the exact mob spawning rules. This would have the benefits of:

1. Providing a benchmark for the developers when modifying the code to see if spawns are correctly implemented and hopefully reduce the number of future spawning bugs.

2. Provides beta testers and players a reference to determine if a change in spawning mechanics is intentional or a bug, which would both reduce the number of bug reports for WAI features, and hopefully reduce the number of bugs making it into the release if caught in a beta version.

3. Provides players a way to adjust builds for changed spawning rules when such are intentional.

Apologies if there is such a reference, which the minecraft Wiki clearly is not, but I've not heard of one.

What you're suggesting is that Mojang ought to publish its internal design documentation. Yes, it already exists and the developers and internal testers definitely are using it in the ways you've mentioned. But it's not public, and I doubt it ever will be in anything like the level of detail I think you mean. While it would be interesting to discuss the reasons, the bug tracker is not an appropriate place to do so.

Incidentally, perhaps I should mention that I don't have access to the internal design either. What I said about raid spawns above is inference from thinking about how spawning a raid is different from either general mob spawning (animals and monsters) or structure spawns (villages and ocean monuments).

This issue will be active again as we have reverted the fix for MCPE-59682 - we are working on a solution that will correct both situations.

A full release came out today with this bug in it. I was really expecting this to be fixed before you released another version. The internet says this is the last 1.14 build and everything going forward will be nether update betas. Considering this is a pretty serious issue, can you confirm that you are planning on patching this before the nether update? Thank you. 

I was forcibly realm updated to this and it's broken everything I have once more (such as having creepers spawn on my spawnproofed raid farm because now leaves are spawnable).

I recognize https://bugs.mojang.com/browse/MCPE-59682 as a problem, but there were workarounds and the community had been used to it for a while. Especially when spawnproofing a large area with trees, this is very hard to work around.
You'd think that rather than pushing out a patch to fix something by breaking something else, one could wait a bit longer and simply fix both, but the phrasing of the patch notes implies that we won't be seeing the true fix for quite a while. I suppose it isn't as high priority as marketplace updates/fixes.

Think it's time to take a break from Minecraft. I have too many things to do with my time to waste it on this.

I can not believe that Mojang is reverting a bug fix and the result will completchange the basic core concepts of the game and that it is being reverted before a more thorough fix is completed. On top of that, the reason it is being revert according to the patch notes is seemingly to allow for players to make YouTube mob grinder farms.
This has been working fine and shouldn’t be revert until a fix for both problems exists at the same time. Disappointed. I don’t want to play Minecraft with creepers falling out of the sky.

Agreed, my base is built high up in the trees of a mega taiga biome. Think the Ewok Village from Return of the Jedi and you'll have an idea. It's mostly open air, as in no actual house structure but a network of platforms and bridges running through the tree-tops, which has been completely viable for the last 2 years. Imagine how much fun this update is going to be for me. It could be unplayable. Furthermore, we didn't even get the bee parody features from java in this update. On Java bee nests can spawn when you plant a tree. I was looking for that in the changelog today and didn't see it. They also made a great change to elytra takeoffs on Java that Bedrock did not get. Yeah, this better not be the last 1.14 build. Are you reading these comments, Mr. Wells? 

They really need to fix this bug. Not work over it and hope for the best. This is breaking all the areas that I spawn proofed and took so much time to work on. Stuff like this really makes me want to cut my losses and just delete my game till they get a real fix out. Updates to the other areas of the game won't mean anything if my base isn't usable.

Nobody is more disappointed than me that this fix was reverted. Like many of you, I took a break from my survival world when this bug was introduced, and now I'll have to take another until it's fixed again, which is especially frustrating for me because I just recently started a new survival world with the best seed I've ever found, so I'm very eager to explore.

Unfortunately, I have no information about how soon a new fix might be released, but bear in mind that this issue was the main reason 1.14.1 was released as a hotfix. Its impact is well known and I'm sure the developers are scrambling to get another solution ready ASAP.

@unknown and @unknown, don't let the title of MCPE-59682 mislead you. Although it was reported as an issue with mob farms, it actually affected mob spawning everywhere and was preventing monsters from spawning in caves as well. That's perhaps even more disruptive to gameplay than this bug was, and I imagine it's why 1.14.2 was also released as a hotfix.

@unknown, I'm not sure where "the internet" says this is the last 1.14 build, but I wouldn't put much stock in it. I have never known Mojang to make an announcement of that kind, and even if Mojang did say it, they probably changed their minds when they realized this bug was reactivated.

Thanks for the comment Auldrick. You are always appreciated.  No nothing official just MCBedrock.com and the way people are talking on reddit. Just hoping they are all wrong in their assumptions.

On a somewhat related note... any chance you want to share that seed number? 😁

The “last build” statement was made about Java 1.15.2, here: Minecraft.net/en-us/article/minecraft-java-edition-1-15-2
It has nothing to do with Bedrock or this hotfix.

I shouldn't be doing this on the bug tracker, but... -766684758. It has some version of almost every kind of biome within a couple thousand blocks, including a mesa and a jungle, and you spawn on a cozy little plain peninsula next to an ocean, so early exploration will be easy. The only common biome I didn't see on a quick overview was a savanna, but I'm sure it won't be hard to find. There's also a village not very far away. Note that I don't check for strongholds, monuments, mansions, or mushroom islands in seeds I'm pre-screening, so it may not be up to your standards.

Mansions and strongholds aren't that impt to me. That sounds quite nice actually and it will give me something to do while I wait for a fix. Thanks! 

GoldenHelmet, I was refering to this: https://www.mcbedrock.com/2020/01/28/minecraft-pocket-edition-bedrock-1-14-20-update-released/  as well as reddit conversations. Nothing official, which was why I wanted to know. 

Why didn't they just leave it for now? We found fixes for bottom slabs on mob farm roofs, multiple options in fact.

We easily solved the slabs on the roof problem, what are we going to do with this? There's no replacement for Leaves and Glass. On top of that, this gave us a way to easily spawn proof entire Y coords with slabs... which was pretty great.

Now any farm that uses leaves and glass for spawn proofing is unworkable. When any farm broken by bottom slabs could've easily been fixed with carpet or torches on the roof. The farms that use glass and leaves can't be easily fixed. I'd like an explanation as to why this was seen as a good idea. We literally had better solutions and you took them away for no reason because your mistake was ridiculous so you just had to undo it. I could've worked with that mistake better than this one.

All you had to do was leave it until you found a better solution. Get it, "leave it" Leaves... haha? No?, whatever.

You do realize wasting people's time like this and causing re-work and unworkable farm designs will frustrate them to the point where they stop playing right? How that's in your best interests, I have no idea but you might want to re-evaluate your testing program to avoid this in the future. Just a thought. 

@Christopher how interesting, it looks like that website interpolated the Java last build statement into their announcement. The official changelog does not include it: https://feedback.minecraft.net/hc/en-us/articles/360038848252

@Travis Pluff MCPE-59682 affected most all non-solid blocks, not just slabs. It applied just as much to leaf and glass roofs. And it prevented not only mob farms from working, but also things like animal spawns under trees. On the flip side, the carpet workaround for MCPE-59682 should still work, at least in local worlds—see MCPE-58670.

I can understand why Mojang chose to revert the previous fix if it was causing a lot of other problems. However, I don't understand why the fix for this specific problem is so difficult? If the code is at all well structured, there must be a well-defined place where a monster "spawn attempt" is made for a block. This would be where the light level is checked since monsters can't spawn above certain light levels. Why can't they simply put a check for blocks such as leaves, glass, etc. at that point? That would not prevent additional spawn attempts at lower Y values. Even if that was a temporary fix until there is time to work out something better it would address this issue.

The Minecraft code is a lot more complex than most people, including outside programmers, probably expect. I say that as a former developer myself who, while I don't have access to the code, have often been surprised by descriptions the devs have shared about how some of its algorithms work. "If the code is at all well structured" suggests that you're thinking about how you would have designed it, but you and I have the disadvantage that we usually play the game a certain way, and our design doesn't necessarily accommodate requirements the game has to satisfy but which don't affect our play. Our parochial view makes it seems simpler than it really is.

A good example of this is what support for add-ons does to the code. Behavior packs abstract thousands of parameters used by the game's algorithms, which means that a straight line reading of the code can't really tell you much about how the game will behave in a specific situation. Light levels and allowed blocks for spawning are some of what the behavior pack encodes, so reading the code alone would tell you literally nothing about which mobs can spawn at a certain location in a certain world. To find that out, you'd have to analyze all the applied behavior packs, determine the highest priority one that includes the relevant parameters, and look up those parameter values. The game actually does something like this, and all that logic complicates the code.

Re-resolved as Fixed because it turns out that the fix for MCPE-59682 did not revert this fix after all.

Played a bit last night and didn't see anything in my trees. I figured I was just at cap or getting lucky, but this is wonderful news! Can't wait to play tonight after work! 

I would like to report this as broken again. Buttons on top of blocks don't prevent spawning again (same with string but is intentional I think?)

@Amdeo Meure: please create a new ticket describing your issue in the current version.