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MCPE-29548

Relogging can cause observers to emit pulses

Edit by @unknown, updated by @unknown:
Original test world was unreliable because it had the observer looking at lit redstone dust across a chunk border. Test world and description updated to include other blocks on November 2, 2021.

Observers looking at several kinds of blocks emit a pulse on world reloading. The attached test world demonstrates the bug. The following blocks were tested in 1.17.41 Hotfix:

Block

Triggers observer pulse on relog

Lit redstone dust

unlit redstone dust

Redstone torch (lit or unlit)

Repeater (powered or unpowered)

Comparator (powered or unpowered)

Empty single chest / barrel

Empty double chest

Chest / barrel with item in it

Dropper (empty or with item)

Item frame

Glow item frame

Tripwire with mob on it

Pressure plate with mob on it

inconsistent

Mob head

Campfire

Cauldron

Steps to reproduce:

  1. Open the attached world.

  2. Close and open it again.

  3. See what the dispenser does.

Strangely, the pulse is too short (0 ticks maybe?) for dispensers to trigger so you need a repeater to make the pulse a bit longer.

Linked issues

MCPE-191171 Copper bulb Resolved MCPE-184491 Copper Bulbs turn off Resolved MCPE-186395 Observers emit impulses when reloading the world Resolved MCPE-187691 Observers can fire on world load Resolved MCPE-190175 Issues when loading the world and checking redstone systems. Resolved

Attachments

Comments 36

Thanks PHO! I didn't perform enough testing to realise that it was only due to the observer, and I'm glad you've deduced that.

I can confirm in stable 1.6.1 that it is `redstone_wire` that is powered (error message of `/testforblock <pos> redstone_wire 0` says about a different data value).

Edit: Using a normal Piston for the output can also detect the result easily (put a pushable block on its face)

Still affects all updates until 1.11.4

Also affects 1.12 and 1.13 updates

(Tested before reported - from 'Technical Bugs List' https://docs.google.com/document/d/1nziKYzCr4pBdCRj2gIMlfr9MVdWHd6HyafdiBHx9F0c/edit)

This issue happens in 1.15.0.53 also.

26 more comments

The addition of copper bulbs has really exacerbated this issue. I've made a few designs now with observers toggling copper bulbs, and they work fine when the world stays loaded but (sometimes, unpredictably, in some chunks but not others) lose their minds on save/restore since the bulb state gets toggled when nothing happened. At first I thought it was an issue with save/restore of copper bulbs themselves, but I eventually traced it to this long-standing observer bug.

Attached world ("MCPE-29548") with a copper bulb repro case. Observer watches redstone dust (toggled by lever) and powers bulb. The mechanism does not cross a chunk border.

Expected behavior: redstone dust and observer bulb stay in sync (both active or neither active) including across world save/load.

Observed behavior: powering dust then relogging results in out-of-sync state (dust powered, bulb off).

I'm guessing this probably also relates to MCPE-180268 (found it through mutually related bug MCPE-179848)

(updated with behaviour for barrels, which matches single chests, tested in 1.21.51)

Still a issue

Also observers pulse on relogging when facing redstone powered by a storage facing comparator

GunsAndChips

(Unassigned)

94243 / 95333

Confirmed

Windows

Windows 10 Pro

redstone

1.18.10.21 Beta, 1.18.0.24 Beta, 1.17.11 Hotfix, 1.17.0.50 Beta, 1.16.220, ..., 1.21.2 Hotfix, 1.21.22 Hotfix, 1.21.23 Hotfix, 1.21.40, 1.21.51 Hotfix

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