Stable version I believe. I stepped on and off the reverse switch a couple of times in rapid succession.Moving this back to bug reports as it seems like it's resurfaces again
@CatBug : Did you step in front of the block that went outside of the puzzle at some point, causing it to move back a bit as to not crush/move over you? Or were you playing multiplayer, having a friend pushing the block unto you, or you pushing the block unto him?
Also which version are you on? You can see its name in the top left corner of the start menu