Sorry to hear about that. The code is there to lock in the mouse and if not you could try setting the game to full-screen. In all my testing the mouse was fine though. Maybe if you press Escape it can do that I'm not really sure to be honest.
Thanks, the game starts with the mouse locked in but it unlocks after the first time I press Esc. How do I enter fullscreen? I tried Alt+Enter but it doesn't work...