mojira.dev
MCPE-175206

Pistons pushing/pulling/breaking blocks may teleport player to 0 on one axis

From @unknown:
(The test world shared by ItsRichHeart breaks after the fix to lava-water interaction in 1.20.40, so I made a new one.)

Steps to reproduce

  1. Load

[media]
  1. Flip the lever on the contraption.

  2. Move to near the side of the lower row of blocks and wait a few seconds.

Expected result

Nothing happens. You just watch the block feedtape cycle.

Observed result

You get teleported to X = 0.


After the latest update v.1.20.30

My moss farm wich is in the style of the youtuber silentwisper, now teleports me about 60 blocks downward when i turn it on. 

Linked issues

Attachments

Comments 12

[Mod] OcelotOnesie

Please attach a video of the issue and update the description to include steps to reproduce. The following format is recommended:

Steps to Reproduce:

[Step 1]
[Step 2]
[Step 3]

Observed Results:
[Describe what happens]

Expected Results:
[Describe what should happen]

Notes:
[Any further information you can provide about the bug.

Please also specify which device you're experiencing the issue on.

migrated

https://youtu.be/hVImUoB0lOo
Here is a link to a youtube video of me having this issue. 

Steps to Reproduce:

Have a moss farm, containing a stone generator and bonemealing a moss block. 
Turn it on. 
Be teleported about 60 blocks downward

Observed Results:
Auto teleported downward when near operating moss farm.

Expected Results:
Nothing should happen when i turn on moss farm. 

Notes:
Im on v.1.20.30 bedrock edition on a ps5. 

GoldenHelmet

I have seen two other reports of this issue in Discord chats, both related to cobblestone farms. Moss and cobblestone farms have a lot of pistons firing at at once, so I would guess there is an interaction happening between the player and pistons several blocks away. In all 3 cases so far it is only one coordinate that changes, and that coordinates is set to 0. The coordinate change likely matches the direction the pistons are pushing. In the video linked by the reporter here the pistons are pushing down and the player is teleported to 0 Y. Note that the displayed coordinate is -2 Y because this is a an unadjusted server-side position update, so it is the players eye position that gets set to 0.

Here’s an example where the player is teleported to 0 X. https://cdn.discordapp.com/attachments/600409597009854464/1154151680804393021/cachedVideo.mov

GoldenHelmet

Rainbowtraib: does this only happen on a realm? The other reports I’ve seen both were from realms.

migrated

Here is a video of me having the same issue: https://youtu.be/bgRygJ9sLI0?si=kXgyuKNBODDWbJ81

I am playing on a Windows 10 realm in v1.20.30. The farm I am using in the video is by centi. Video/world download: https://youtu.be/_7sburjuwtg?si=KOd6CMBXkURQc9zV

2 more comments
ItsRichHeart

Steps to Reproduce

  1. Open 

[media]
  1. Flick the lever of either "South" or "East"

  2. Stand there for a couple of seconds (5-10 seconds) and turn the contraption off

  3. Flick the lever of either "North" or "West

  4. Stand there for a couple of seconds as well (5-10 seconds)

  5. See the result (and use the commands to teleport back)

Observed Results:

When doing step 2 and 3, nothing happens
When doing step 4 and 5, you get teleported

  • For the "North" side, you get teleported to z=0

  • For the "South" side, you get teleported to x=0

Expected Results:

When doing step 4 and 5, you should not get teleported, just like in step 2 and 3

Notes:

  • For help on replicating the bug, see the attached video for a visual guide

[media]
  • The bug even happens if the command blocks are not there (simply pushing the block already creates the observed results). They are only there so it can keep on placing blocks

  • When standing above the pistons (y-level of the player is above the y-level of the piston), the player does not get teleported. Only when the y-level of the player is at the same level or below it

  • After further testing, at negative x and z coordinates (e.g. -1000, -1000) instead of teleporting back to x = 0 or z = 0, the game simply rubberbands and teleports you constantly back, see this imgur link for a video: https://imgur.com/a/hWaEtZX

GoldenHelmet

This can be triggered by a block conveyor as well, which shows that the lava, water, and block conversion in the test world are unrelated:

[media]

Based on careful scrutiny of all of the repro videos, I think the bug triggers in the tick when a retracting piston attempts to remove its extended arm and, if it is a sticky piston, any attached movingBlock. If another block is being set in the same tick into the same place where the piston arm or movingBlock is being removed, then there is then a chance that the player gets teleported.

The payer being teleported also seems to correlate with the creation of a glitched movingBlock. You can see this by turning off the command blocks that break the cobblestone in the test world. When the blocks are not being broken, then each time you get teleported, one of the lines of cobblestone stops advancing. After all 6 lines of cobblestone stop advancing you no longer get teleported. At that point some of the "cobblestone" continues running the movingBlock animation when the pistons extend and retract:

[media]

I would explain the glitched moving blocks and player teleport this way: when the bug triggers on the retracting piston, it mini-crashes the piston's block update function, cancelling the rest of the updates that that piston was scheduled to make in that tick (so some of the blocks in a row of moving blocks do not get converted back to normal blocks) and overflowing junk data into the player's position. That's just a hypothesis of course! It does suggest a possible relation to MCPE-65970 though. Perhaps some work was attempted on that issue, which caused this one?

bigCRAFT

Still present in latest previews.

migrated

Just had this same issue with a trident killer for a mob farm.  Happened regularly within 5-7 seconds of starting my 3x3 trident killer.  It does use carpet to avoid the dead space, so the piston block updating makes sense.  IOS Minecraft Bedrock v. 1.20.51.

migrated

still present in 1.20.51 (windows 10 edition)

migrated

(Unassigned)

1136144

Confirmed

Multiple

1.20.30, 1.20.31 Hotfix, 1.20.32 Hotfix, 1.20.50.22 Preview, 1.20.40, 1.20.41 Hotfix, 1.20.50, 1.20.51 Hotfix

1.20.60.24 Preview, 1.20.60

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