Hitting the top of an activated piston will drop a piston while in Creative mode.
A bit like the bug where hitting the top a door in creative mode dropped a door.
Related issues
Comments
CubeTheThird
Duplicate of MC-149, please use the search function to see if your bug has already been submitted. Currently over 42% of tickets are being closed as duplicate.
Can confirm. Note that for this to occur, one must simply destroy the head of the piston while it is activated, regardless of direction.