Minecraft wiki entry for Piston, associated text: Sticky pistons stick to a block only when retracting, so a block next to the piston head can be pushed aside by another piston and sticky pistons cannot hold falling blocks horizontally against gravity. In Java Edition, pistons finish extending early and start retracting if given a pulse shorter than 3 game ticks (1.5 redstone ticks; 0.15 seconds). These shorter pulses cause sticky pistons to "drop" their block, leaving it behind when trying to push it with a short pulse. Also, this causes the block to end up in its final position earlier.