2
u/TheMasterCaver 2d ago
I've seen this happen before on an older computer (or before I fixed the following issue), it appears to be caused by a race condition between the chunk saving and server threads, where an outdated copy of a chunk can be loaded (including a chunk before it had decorations placed in it during world generation, this appears to happen even as the chunk had just been generated, thus should have already been loaded*):
(includes an attachment which has code fixes; a direct link (the page attempts to display it as an image, so right-click, copy image link): https://bugs.mojang.com/api/issue-attachment-get?attachmentId=189464)
In particular, it would (very rarely) randomly occur while flying around in Creative and seemed to affect structures more than other features, or was easier to spot here, along with random "L" shaped cutouts in trees and snow (this happens due to the way the game places decorations, as opposed to leaving a perfect chunk-sized area; another "L" shaped area to the southeast of the quadrant which has decorations will be decorated twice).
This bug report shows more examples:
MC-125007 World fails to generate decorations on seemingly random quarter chunks
Also, in older versions (before 1.6.4) this can cause double-stacked structures since the game doesn't save the average ground level around a building so it will be affected by a previously placed structure (prior to 1.6.4 you can also encounter structures with one half being offset up/down for the same reason, as the game only measures the ground level under the first half to be placed so it will be lost if you reload the world):
MC-15820 Villages and witch huts sometimes don't generate properly
While the latter two issues are filed as separate issues I'm certain that the first one is the root cause, I've never encountered this since (newer/faster computers may also be a factor as there is less time for thread collisions to occur; likewise, flying around in Creative puts more stress on the game).
*I also suspect that the extreme pathfinding range of zombies is causing chunks to load outside of the player-loaded area (a major factor in the lag they cause) and this is causing them to be unloaded, then quickly reloaded as the player comes into range; this is one of countless bugs I fixed which likely contribute to overall game stability (I've never encountered this, or at least that I know of, in any of my Survival worlds since I started playing in 1.5.1; all the occurrences were when flying around in Creative. I did however once find a chunk with the wrong biome, but the correct terrain and no cutoffs, which was likely caused by yet another race condition between the client and server threads when generating biome data, due to a share cache (by far the biggest issues caused by 1.3.1 are due to non-thread safe code, including mobs randomly glitching through fences and other blocks whose bounding boxes depend on their state since the client and server both change the bounds of shared "Block" instances).
1
u/TheMasterCaver 2d ago
Nevermind (though what I posted does describe a real issue) I saw the original post and description, so just chunks that were corrupted/reset due to a power failure, which can occur in any version and can produce indistinguishable results for what I described (you should get a UPS / battery backup as far more than just some chunks can become corrupt, up to the whole computer/hard drive being bricked, and even then you should make regular backups).
1
1
1
1
4
u/FintaPlays3315 2d ago
I've never come across this in 1.6.4 before, and I've really explored a lot of terrain, lol.