When a piston is rapidly extending and retracting in a redstone loop, it is possible to place blocks "through" the piston, inside its movement zone or where it should be solid.
This allows players to place blocks inside or behind a moving piston arm, which should be impossible due to collision rules.
Steps to Reproduce:
Create a fast redstone clock that causes a piston to open and close rapidly.
Try placing a block (like dirt or stone) at or behind the piston head.
❗ The block can be placed through the moving piston, even though it should be solid during movement.
Expected Result:
You shouldn't be able to place blocks through a piston that's currently moving or extended.
Tested on:
Minecraft Java Edition 1.21.7
Singleplayer + Creative and Survival
Vanilla behavior (no mods or plugins)
Environment
Windows 11 Pro
Linked issues
Attachments
Comments 4
The piston seems to have the hitbox that disables placing blocks through itself when it is fully extended/retracted or is being extended (expected) but it doesn’t seem to have that hitbox when it is being retracted (unexpected). If you try targeting any block through the piston, Minecraft sees you targeting that block when the piston is currently retracting.
This might relate to:
Thanks for your report! This is a duplicate of MC-103071, which has been resolved as Won’t Fix.
And there was another report about the same issue from one of my other emails which was marked as patched, but the bug has reappeared.