The Bug
In certain scenarios where a horizontal piston is unpowered or updated to retract, if a block with gravity is on the piston, it is broken.
What I expected to happen
When the piston unpowers, the gravity block (sand) falls to the ground and lands on the floor
What instead happens
When the piston unpowers, the gravity block breaks. It happens instantly, perhaps before the block can turn into an entity.
Steps to reproduce (as shown on setup.png or variations.png)
Place a piston
Power the piston using a redstone wall torch above it
Place a gravity block on the piston head (tested with sand, gravel, anvil, concrete powder)
Break the torch
Watch the falling block break before it can fall to the ground
Another way to reproduce (as shown in the background of setup.png)
Place a piston
BUD power the piston, using a redstone block for example.
Place a gravity block on the piston head
Break the redstone block that is BUD powering the piston
Update the piston (by placing a block next to it, for example)
Watch the falling block break before it can fall to the ground
Additional info
Broken in 1.19.2, 1.17.1, 1.16.5, 1.15.2
Working in 1.14.4
Attachments
Comments 6
This could be a clone of MC-143893
I noticed it only happens when you update both piston and gravel at the same time.
Updating the gravel and piston at the same time using the following things made the gravel break:
placed or broken blocks (by the player's hand, updating a block that shouldn't be allowed to be on a piston, or landing falling-blocks, lighting TNT with flint&steel)
noteblock, state-changing redstone wire, unpowering redstone torch
powered rail, activator rail, or detector rail (eg. by placing one next to the piston and one next to the gravel, on a slope, connected)
unpowering dispenser/dropper/hopper, trapdoor, fence gate (only updates gravel, not piston, so you need to update the piston at the same time using something else like a noteblock)
level-changing cauldron/composter, eaten cake, charge-changing respawn anchor, (un)lighting furnace,
but not:
an extending or retracting piston or piston head
chest, skulk sensor,
redstone repeater, redstone comparator (any direction, in/out of the gravel block, in/out of powering the piston)
growing sapling -> tree (using worldedit to set a sapling above the piston)
moved block (using another piston to push blocks between )
(redstone lamp, chest, shulkerbox, )
I assume this is due to the update order, hence why repeaters and moving blocks don't update the gravel at the same time as the piston ❓ .
Using this same method, I tried updating an upward-facing piston and gravel simultaneously, but I couldn't reproduce it, so it seems to only work horizontally/sideways.
This also means that, if you have a pile of sand or gravel, and push the bottom of the pile by activating the (non-sticky) piston with a 1-tick pulse, it will both push the gravel on the face of the piston, and break the gravel right above it when retracting.
Thank you for your report!
After consideration, the issue is being closed as Working as Intended.
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Wow I think this might actually be unintended. I tested it out with different circumstances:
https://youtu.be/fRnyUkKx5DQ