Any game mode, when a redstone block is on top of a piston and then you give the piston power the piston will work, then when you take the power away the piston stays like it still has redstone power when it does not.
this bug has been in the game for a long time, it came in 1.5 and is still in the game.

found by: Callummine

you can see the redstone piston bug down below ↓↓↓