Moderator Note
"Block lag" is not a bug, it is a symptom of one of myriad causes. There are multiple things you can try:
• Turn down your render distance (to 8 or lower)
• Turn VBOs "on" in video settings
• Make sure you don't have any possibly lag causing things, like too many entities
• Update your graphics card drivers
• Give Minecraft more RAM (with regular resource pack, 2 GB is enough)
• Upgrade your hardware
When the player is clearing blocks and clears one or two blocks they are instantaneously regenerated after those blocks were cleared. The same happens when placing blocks, they disappear for a while at first.
The internal server is having low TPS and therefore registering the block-breaking action from the client very late. This leads to the client re-displaying the block again, until it gets the confirmation from the server that its actually broken, seconds later, or not at all. At the end, the block is either broken or still there, on both client and server.
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Is this singleplayer or multiplayer? Is it one area that happens or the entire world? Do new worlds do this or just one specific one?

I'm getting this very rarely on a local server. As OP describes, a block will instantaneously reappear when trying repeatedly to destroy it. If I turn my attention to another block, and then try the problem block again, it destroys and stays destroyed. Mine is a newly generated 1.4.2 world, SMP.

it is on a new world that i made right after the "pretty scary update" And it is on single player

now i just died because i PLACED a block in the lava and it disappeared right after i placed it.

Is this still a concern in the current Minecraft version? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.

If it the same thing as in the video below, then it happens in 1.4.6 too.
http://youtu.be/O5lZnEqrKh0

I produced a version of this bug in single-player survival mode 1.5, while mining obsidian under a thin layer of water. When I finished mining the obsidian block, it would flash and instantly reappear as a whole block. I mined the block again and it did the same thing. Moving away would eventually cause the block to break and drop the item block normally....happened for a number of blocks, but not all of them.

I get this a lot in single player survival when using enchanted tools that break blocks quickly. I find that the most common way of running into this very annoying bug is by using a diamond shovel enchanted with effficiency IV on some dirt blocks. This bug still occurs in 1.5.1 too.

I've had this same issue as of Snapshot 13w24b.
Fix: (Worked for Me):
Open the world to lan and for other players settings, turn cheats on and I broke the block and it worked, I don't know how this is possible, but the block does not reappear and now breaks normally and drops the block normally. I was thinking maybe lag from the singleplayer server? I'm not completely sure but it worked.
EDIT:
After turning on your lan world and activating cheats, you may have to Save and Quit to Title and go back to your singleplayer world.

Is this still a concern in the current Minecraft version 1.6.4 / Launcher version 1.2.5 ? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.

It still happens with 1.6.4. Blocks sometimes take 2 or 3 tries to keep them gone. Sometimes they reappear then disappear after a second or two (local server multiplayer).

On 1.7.2 SMP I noticed that the block disappears for the client but it is actually there, not allowing the player to move through it. I don't know about SSP.

I had a similar issue with a disappearing block in 1.7.4 on the boundary between a tundra and extreme hills edge biome. Not sure if that's relevant, but I was using an efficiency IV diamond shovel on dirt when it happened. I was in SSP running on a MacBook.

It might be because the breaking speed of a pickaxe has somehow increased so Minecraft thinks you haven't broken it yet so it replaces it.
Enchantments like Efficiency 4/5 speed up the mining. Haste also does this.

Still happening 14w04b, I'm experiencing similar to what Jonathan mentions - Haste II plus Efficiency V makes this very common. It also seems to be aggravated if you switch tools quickly, i.e. speed mining stone with a pick axe, switching to shovel to get gravel out of the way, and switching back to pick axe will sometimes leave whatever the shovel was getting in place. This isn't the only way it happens, just seems to make it much more common for me.

I agree with David Truog. I'm currently in 1.7.4 clearing a large area of the nether with Efficiency V shovels and pickaxes. This bug is happening to me a lot, and is exacerbated by switching between the shovel and pick (when I switch from mining soulsand to netherrack and vice versa).
When it happens the block looks to disappear client side, but when you walk into its space it jerks you around like your client is trying to move you forward but the server keeps resetting your position to be outside the block. The easy way to fix it (without relogging) is to attempt to place a block in the offending space. The block you place will not be placed, but the block originally in the space will reappear and the block-placing noise will not occur. That's the callsign of this bug. I've seen it recorded in several videos of youtubers I watch as well, mostly Etho and Docm77.

@JONATHAN_89 I don't think so, this bug still happens with an unenchanted stone pickaxe.

@Lane Yes, it also can due to lag.
But enchantments can make it more common.

It does the same in single player, should not be lagging there except for snooper or related connections...

This is obviously an issue again and it makes it completely impossible to ever play survival in the latest snapshot. I guess https://bugs.mojang.com/browse/MC-55532 is a duplicate, but it's different causes. This really needs fixed. This is probably one of the worse bugs we have right now. This is issue looks more like for enchants, this is just everything.

Confirmed. I have this bug a ton. Mostly in CTM maps.

im having the exact same problem but with 1.7.10.

Impossible to play the latest Minecraft versions. :|

confirmed for 1.8-pre 2

yeah I stopped playing this whole series because of this bug. even if I bring my render distance down to 8 chunks, turn off all the fineries, it still happens constantly. I've been waiting 10 minutes for sand I placed to fall... another few minutes for other blocks I've broken to finally disappear... then a few more minutes to be able to be able to pick up the pieces. Just logged in to confirm it's still happening.
Windows 7 Pro SP 1 (all updates)
Java 7 u 67
i7-920 (1st gen)
24gb Ram
On a SSD (Samsung Evo 1tb)
Asus Geforce GTX 760

This also happens to me in 17.10. Both the server and client are hosted on a Windows 7 PC; 8gb ram, 3.0Ghz dual-core AMD Athlon II X2; Java 7 update 67.
I believe it results from the server not realizing you've switched to a shovel, and the blocks are broken (thanks to a combination of diamond quality, efficiency, and beacon) before the server registers they should break that fast.

Still happens in 1.8 official release. Although for me it seems to only happen after many chunk updates.
Win 7
4gb RAM, 2 allocated, nothing else running.
AMD Radeon HD 6320 Graphics

Still happens for me in the official 1.8 update, seriously makes the game unplayable. Specs: windows 7 8GB Ram AMD FX 4100 Quad core processor AMD Radion HD 7450. 64 bit Java

yeah the game is unplayable. it even lags if I turn all the detail settings to minimum and set the chunk render distance at 2 chunks. This game's just broke and has been like this ever since they changed single player to be client/server. I think if they were going to fix it they would have. I'm going to try some different versions of Java. Why this game is still crippled by the poor choice of Java for the language is mystifying.

I had this happen briefly before, but now it's back. When I mine a block, it disappears, then reappears. Then, 1 to 10 seconds later, the block disappears again and the item is dropped. The game was working fine all day, but it started happening about an hour ago. When I restarted my computer, it made the delay even worse. Happens with all tools, but only occurs when mining blocks. Ladders, torches, etc. work fine.
Version 1.8 vanilla. No mods, no textures, etc. Windows 7 Home Premium x64, 8GB RAM, Java 1.7.67 x64 (happens with x86 too), Quad Core Intel i5-3210M. Intel HD Graphics 4000.
Update: It seems I left my dispenser turned on at my chicken farm. So 4 gold swords, 2 iron swords, and 15 stacks of feathers later, I am no longer having an issue.

Singleplayer games have the possibility of lagging since LAN worlds were added, because this made the client act like a 1 person server. To fix this, Mojang needs to fully disable the server when the game is not open to LAN.

@StevenNL2000, disabling the internal server wouldn't make any sense. When "LAN worlds" were added, the way the client functions was completely changed. It works as 2 separate sections: the client (which performs tasks like rendering), and the internal server (which does things like chunk generation). This internal server works essentially the same way as though the client was connecting to an external server. To disable this server means half of the game components wouldn't be present, and it wouldn't work.

That is probably true, but this is almost certainly caused by LAN worlds, as the client was doing all tasks on its own before they were added. The internal server apparently has the possibility to desync with the client (lag).

I had that block reappearing problem. I have tried anything with no success. In the end, i killed most of my animals and the problem disspears. I don't know why, but it works. That isnt logical, cause that problem was everywhere on the map. And yet that works for me.
I hope that it works for you too.
Excuse me for my bad english 🙂

I still have this happening but I find that it reduces if you set the memory to 4gb and the part of the cache (I think it's at the end of the java options sting in the launcher profile currently at 128 to 256M (cache?) Java 1.8.20 seemed to clear it up a tad too without introducing any other noticeable bugs I could find in a typical survival run. Takes forever to load the first chunks when starting a new world, though.

Try and upgrade to Windows 7 or 8.

Did anyone notice that the comments here describe two completely different phenomenons?
Block reappears after client broke it - then finally breaks after about a second. Caused by server overload / lag. Fits the bug description on this page.
Quick mining e.g. with Efficiency-enchanted tools leaves block in place server-side but client thinks it's gone. Bad collision when player runs into it. Shown in the video posted by Marios and further described in the comments by Apocalypsing, William McDermott, JONATHAN_89, [Mod] fienxjox, Roachy, and Classic. That bug does not belong here and is actually reported in MC-5694 and MC-7409.
I hope the mods can untangle this somehow.

I experience this bug when I am playing version 15w37a. In version 1.8.8 all is ok.

Invalid
This is caused by the system not being able to keep up with the game. The report is too generalized, and does not outline any potential causes. It might have been better in earlier versions for you, yes, but the game changed over time. If you have this issue, turn down your render distance and make sure there is nothing too complex running in your world (or too many entities).
Please comment if you don't think this applies.

I just want to add some general advice to try before asking for any help diagnosing performance problems in Minecraft:
"Block lag" is not a bug, it is a symptom of one of myriad causes. Before anyone can help you diagnose a specific problem, I think you need to go through a checklist like this:
•turn down your render distance (to 8 or lower)
•turn VBOs "on" in video settings
•after doing that, exit minecraft, restart it, and then
•create a new default world
•let the world load for 30 secondsNow, did the block lag in that fresh world go away? If so, then the problem was probably one of
•you had your render distance too high
•you had the wrong VBO setting
•you didn't give the world time to generate (the terrain generator lags the game a bit at the very start)
•something about the other world you were previously playing on is laggy (e.g. too many entities, chunk corruption, 1.7 chunk conversion, ...)If the problem persisted in the fresh new world after performing the original checklist above, then you need to take a screenshot of the F3 debug screen, which can help diagnose other issues, such as
•bad graphics card
•non-64-bit java
•insufficient memory
•other tasks on your computer throttling CPU/diskBut it's not necessarily "a bug" in the game, usually it's a user misconfiguration or insufficient hardware, and without lots of this extra diagnostic info, there's nothing anyone can do to help.

@Brian McNamara: Thank you, I'm going to add a slightly modified version of this to the description.

turning down my render distance and turning VBOs on worked. Thanks!

Got it terribly in 1.7.3/1.7.4. On my LP world, but now only new worlds.

Only when breaking blocks at non- instant speed.

Can confirm, that it's still in Minecraft 1.17.1.
It does this so often that it almost make the game unplayable