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:
Open the attached world.
Close and open it again.
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
is duplicated by 26
relates to 4
Attachments
Comments 35
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)
(Tested before reported - from 'Technical Bugs List' https://docs.google.com/document/d/1nziKYzCr4pBdCRj2gIMlfr9MVdWHd6HyafdiBHx9F0c/edit)
This issue happens in 1.15.0.53 also.
Issue present in 1.21
This is breaking a number of shulker loader designs which are in high demand with the new Crafter block. Hopefully this gets fixed urgently as it makes the Crafter less useful
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)
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.