In an adventure map in SMP, I was experiencing strange issues where the locations of other players seemed to be offset. This would occur mainly in cramped places (on the map in question, in the dungeon at the top of the mountain).
I would notice players passing through walls, and sometimes floating or "swimming" in the ground. At some times, the offset seemed to be so bad that players would be rendered several blocks away from their true locations.
Logging out and back in would sometimes correct this issue, but it would frequently return.
I noticed this issue with:
Players who were far away and made a long journey
Players who were teleported to me
Players who I was with during a long journey (namely, up the mountain in the map)
I was running the server on my own computer, and I was connected via localhost. The other players were connected from various places in different states. As my computer is not very good, I noticed a few "<Playername> moved wrongly!" messages in the console. This may be related, but I did not notice any direct connection between the messages and the phenomenon.
This issue has occurred before, on the 1.4.0 prerelease, as well, and is not an isolated incident.
EDIT: I should also note that this never happens to me on Bukkit servers, whether or not I am the host. A server host I spoke with said he has noticed this extensively and exclusively on vanilla servers when he hosts them.
Video footage can be seen in this Sethbling livestream, starting after a series of teleports at 1:38:10. Note that frequent complaints of players in the wrong position (or "invisible") have occurred throughout the video. This server is vanilla 1.4.6 (or possibly 1.4.7, but the two are interchangeable as only one class differs between the two). Sethbling may or may not be the server host; I'm sure Marc Watson of Mojang can clarify (he was present).
EDIT: Since then, I have realized this effect can be reproduced reliably on minecart entities. Steps to reproduce:
Run your own server
Set up a minecart rail loop with powered rails and a two block drop
Add a minecart, and make sure it goes around the loop
Observe that, after some time (this seems random), the minecart gets misaligned: although it tracks the same path, it may appear floating or offset by several blocks.
In my experience, lag on my system makes this effect more likely, as does moving around.
Linked issues
is duplicated by 5
Comments 23
I've managed to get this now in 1.5 on minecarts, so it's not limited to players. Which is pretty bad, to be honest, but at least it makes it easier to test.
So far I've mostly managed to notice this with the player's not appearing to others after doing teleports. Been there for ages, as far as from beta 1.8. Players mostly appear back when you drop down a block below. Disappearing part seems to have something to do with the entitytracker, in MCP it looked like that player was not in the server's entity tracker after doing a teleport and player positions where therefore not syncronized to other players (until the player dropped a block below and then was added back into the entity tracker).
I found a video where the bug is extensively demonstrated and tested . Also, note at the end the client-side offset arrows. Considering this bug pertains to entity offset in SMP, it may be related, but probably isn't. But all of the teleportation bugs are textbook demonstrations of this bug.
Shown to still exist in this video (at 1:15:36), which I'd say is sufficient evidence that this still exists (even though they're using optifine) when combined with the lack of any protocol changes regarding entity motion. It's not exactly the same setup as in the description, but it is a card going some distance and then getting desync'd.
I've tried to reproduce the issue by having a setup where a villager in a cart goes to chunks that are constantly loaded and unloaded, but I am unable reproduce the issue. Does anyone have a reliable way of reproducing this issue? If not, I will close this within a few weeks.
The video provided doesn't really tell us much about the server itself, it is possible the server had modificiations installed.
It also happened in Etho's LP, some time in episode 518... but I don't recall exactly when. It's worth noting that that's a singleplayer vanilla world, and again it's a minecart. But it doesn't help too much with reproducing :/
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Oh, sorry, I had forgotten about this, as it's been a while since I've dealt with vanilla servers (I will note that I haven't experienced it in Bukkit whatsoever).
However, I recently saw Sethbling livestreaming on a vanilla 1.4.6 server: http://www.twitch.tv/sethbling/b/355261121
At 1:38:10, you can clearly observe that, after a series of teleports, players appear in the wrong positions for Sethbling (including the blaze-suit player sinking into the ground at 1:38:30, and the flying cactus-suit player just before that). Sethbling and other players were also complaining about "invisible" players, and frequent relogs were needed to correct the issue.
So, can this be reopened?