if a redstone clock runing into a piston is left on when the game is closed, the game will crash when the player attempts to open the world.

I left my bone meal sugarcane farm auto harvesting piston on last night, and when I tried to open the world that the sugarcane farm was in, the game would crash. the Redstone circuit consisted of an observer, two Redstone dust, and a piston pointing into the block that the observer was observing.