I'm listening...
You mean the pause-menu?! It's not a bug, it's a feature :)
I programmed it that way. If the player presses [ESC] a billboard with "PAUSE" spawns in front of the player, making the illusion that he is actually in a pause-menu. If you unpause the game with [ESC] it falls over.
I liked this idea but guess many player havn't discovered this "joke"
It's actually possible in all other levels except the few last levels.