Hostile mobs are spawning on/in transparent blocks like slabs, fences, glass, etc.

Top-half slabs don't prevent any mobs from spawning. Only bottom-half ones do.
See http://minecraft.gamepedia.com/Spawn#Spawn_conditions

I know that top slabs don't prevent spawns those are all bottom slabs and the slimes still spawn. Please reopen.

Tested on bottom slabs and confirmed.

I think this bug might be more far reaching than just just Slimes.

I covered a fenced off 22x22 area of bottom-half slabs where I had seen a slime spawn on a flat world.

I couldn't get a slime to spawn (possibly needed more time!) but other mobs were spawning on the half slabs as pictured:

Because of 14022 I suspected that this might be part of a more general bounds checking bug which would affect all mobs, but I had only seen the slimes spawn on the bottom slabs.

Reopened.

Happens for me too, annoying

Please respond and add the current version if you can reproduce this issue.

It still effects 15.4

Strangely enough, I cannot see any non-slime hostile mobs spawning on top of bottom-half slabs in 0.15.4.
I made an 8x8 spawn pad and stood 24 blocks away from it in a flat world. Mobs did not spawn at all no matter how long I waited for. I haven't tested for slimes yet.

They do spawn, so i had to change to bottom half-slabs to a leaves, or put carpets on it, whcih looks a bit awkward (Bottom half-slab with a carpet on it) but at least it does prevents the spawn.
I posted the issue i believe, with screenshots

I have a railroad track built 100% on half slabs 4 blocks below the build limit. All blocks within 1000 spaces horizontally and 60 vertically are half slabs. Hostile mobs spawn on it. Also, I have a roof that is 100% half slabs and my nearby golem farm spawns golems on it. Not sure if golems are considered hostile or passive.

I tested in Win10 0.15.7: built 4 darkened spawn rooms with floors of half-slabs, glass, half-slabs+carpet, and glass+carpet. The only one to spawn anything was the room with half-slab floors, several hostile mobs spawned pretty quickly.

This bug has been reported to our internal bug tracker for further testing and a fix. It is scheduled to be fixed in one of the future updates (no specific date can be provided).

This is a bulk resolve of issues that haven't been updated to 0.16.0+ yet. Please comment below (To open the ticket) and update your affected versions. If you cannot reproduce the bug, please write in the comments so we can resolve it as "Cannot Reproduce". Thank You!

I cannot reproduce this bug on v.0.16.1 on the hard difficulty testing with bottom half slabs, glass and glass with carpet. With a night vision effect for visibility. Fences to prevent mobs getting into the testing area.

On a NVIDIA Shield K1 with Android 6.0.1.

See image "20161118" for the testing area for this bug

Confirmed to affect 0.17.0.2

Tested on Samsung TabPro SM-T520 on Android 4.4.2

If you are refering to upside down half slabs (where the slab makes up the top half of the block area rather than the bottom half), this is normal. Mobs can spawn on these.

Version 1.0 , mobs still spawn on bottom half slabs here is a video to prove it
https://youtu.be/MYU1bt0r_DY

I can get mobs to spawn on bottom-half slabs when they are on another block; it's as if they ignore the half slab entirely. They also spawn inside glass that is on another solid block, again, ignoring the glass.

Attached test world. Notice the glass area too.

They can't completely ignore bottom half slabs because they prevent the mods from spawning beneath the block they are on as can be seen from bug 14022.

Confirmed to affect 1.0.4 on Win 10 64 bit. Not only slimes, but zombies, skeletons, spiders and creepers. Haven't seen witches yet but assume affects them too.

it does

Attached another test world: "Mobs spawning on slabs.mcworld"
On 1.0.7 mobs don't spawn on/inside the following blocks:

• Bottom-half slabs (as expected)

And they spawn on/inside the following blocks:

• Glass (unexpectedly)

• Signs (as expected)

• Pressure plates (unexpectedly)

• Hoppers (as expected)

• Redstone dust (unexpectedly)

• Stone (as expected)

• Top-half slabs (as expected)

• Tripwire hooks (unexpectedly)

Reuploaded "Mobs spawning on slabs.mcworld" to fix a mistake in the floor selection system.

Re-uploaded "Mobs spawning on slabs.mcworld" so you can choose the floor type from 16 different blocks.

It's happening on iOS 10.2.1 as well.

Still affects 1.2.0.18 according to various reports, including MCPE-25053

Affects 1.2.0.22 and 1.2.0.25.

That is annoying, even after an update of 1.2.0.25, still a creeper spawn on my stair only roof and a spider spawn on tree leafs. I have to force myself to play peaceful mode.

I guess there's no need to say that it is still happening in 1.1.5 since it is happening in 1.2, but I will anyway. I spent hours building a large area in the nether with bottom half slabs in my "safe" area and as the roof for a wither skeleton farm ala tango's design only to find mobs spawning in both the "safe" area and on the roof. I was already annoyed because blazes could see me over the walls that only wither skeletons were supposed to see me over, but the spawning on bottom half slabs is a huge issue for the farm. All of this is on top of discovering that fighting the wither absolutely destroys the game with lag which makes the entire farm a wasted effort anyway.

Although the changelog says nothing about fixing it, this doesn't seem to be happening any more for me since upgrading to 1.2.0.31/build 9. Yay! 😃

mobs still spawn on glass block, im currently in beta 1.2 build 9

Still happening in 1.2 official release

Windows 10

The problem returned in 1.2.1 for me.

Can confirm mobs are still spawning on glass, leaves, etc. I'm on a realm server on xbox

Still happening in new update 1.2.2

Update 1.2.2 spawns on at least glass, carpets and stairs!

Confirm still spawning on glass and leaves in 1.2.3.6.

Mobs are spawning on fence gates...

This issue is fixed in 1.2.5.12!!!!!!!!!!!

Tested in creative and survival.

Mobs don't spawn on glass, slabs, stairs, fences, fence gates.
Only spiders spawn on leaf blocks.

The issues with spawning appear to be fixed in 1.2.5.12.

the remaining issue with spiders spawning on leaves is being tracked at MCPE-26107

I've seen monsters spawn right next to torches and glowstone, so light levels should be checked too.

I don't agree with 'fixed.' They are spawning in any light levels..

Joe Smith: A helper noted that your issue MCPE-28426 is a duplicate of this one because all the specific cases you listed could be the result of this issue. However, your assumption that mobs were spawning at too-high light levels would not be covered, so we need a test case that demonstrates that. I updated MCPE-28416 to request a clarification. Please answer there.

This issue is specifically about spawning on transparent or non-solid blocks, and as far as we know that problem has been fixed, so this ticket will remain closed unless a counterexample is reported.

I don't think this issue is fixed. Endermen still spawn on the main island of the End (where the dragon spawns), even if the ENTIRE surface is covered with water. They spawn on glass blocks and on top of the bedrock regardless of light level. They do not spawn on bottom-placed slabs. I have reported it.

This fix has broken parity with Java. Before, mobs could and should have spawned on top slabs as it was a solid flush spawning surface for them. Now, mobs no longer spawn on top slabs. A proper fix would be mobs not spawning on bottom slabs, but spawning on top slabs.

Mobs spawning on glass again in 1.2.13.6

Reopened ticket - mobs were spawning in on glass. (They were spawning in on top-half slabs though, which is better than previously reported behaviour.)

Mobs still spawning on slabs, stairs, glass, fence gates, etc.

Windows 10 beta 1.2.13.8

This is easily reproduced by opening a world in creative and using commands to fill in space with transparent blocks.

Issue still persists in 1.2.13.10

Carpets do not prevent spawns as stated in 1.2.13 changelog
Android 1.2.13.60

I'm playing the console edition (Xbox 360). I know it's on or after TU69-Aquatic Update; I believe it is TU73, because I do have the trial version of the Nightmare Before Christmas Texture Pack.
I am playing on Adventure Mode / Hard Difficulty (world created in Survival).
My seed is -2878103199665976685, and I found a zombie spawner at X 296 - Y 57 - Z 78.

I placed half-slabs on the ground to limit the eligible spawn locations (I left open 3 in the 3 corners and 2 on the 2 far walls for mob spawning) and placed blocks above those spaces (with a 2-tall gap) to keep the spawned zombies stuck in place for carrot/potato/equipment farming. When I removed the torches, the zombies began spawning on the upside-down (lower-half) slabs.
I dug up the half-slabs and replaced the layer of cobblestone beneath them with glass blocks. The mobs spawned on the glass.
I crafted shears, got some leaves blocks from a nearby spruce tree and replaced the glass with leaves. The mobs spawned on the leaves. (I saved after the glass trial, but I did not save after the leaves trial, so the picture shows glass.)

I am not seeing anything in the change logs to suggest they are now supposed to be spawning on transparent blocks. Please re-open this Issue and investigate or create a new Issue and reply to this with the new issue number (so I know where to find it).

Thank you for your help,
Tony

PS - I cannot confirm or deny if this is affecting any other versions or updates.

@@unknown Issues with the Legacy console editions need to be logged in the console edition (project key MCCE) section of the bug tracker: https://bugs.mojang.com/projects/MCCE/summary, as this section is for issues related to the Bedrock codebase (project key MCPE).

This issue has re appeared in the latest beta. 1.14.0.2 

I've got a giant hole with nothing but glasts and bedrock blocks on the bottom. At night, the hostile mobs still spawn..  I've attached a screen cap taken during the day, but you can see the slimes down there. The second is at night. The mobs are not easy to see. I have circled a few.

Update... Issue persists in beta 1.14.0.50.

Mobs are also spawning on leaf blocks. (Dark oak and spruce for sure. Haven't tested others)

@Brad Canney, you should open a separate issue for mobs spawning on bedrock, since bedrock is not a transparent block.

Oh sorry. I should have included an update there too. I've removed the glass for 1/4 of my hole and The mobs don't spawn there. They most be spawning on the glass blocks

@Brad Canney The issue with leaves and glass is being tracked at a new issue: MCPE-54241.

Current issues with spawning on leaves and glass are being tracked as MCPE-54241. You may want to upvote and/or watch that ticket instead.