Is there any reason that mouse grab is disabled in fullscreen mode?
I have multiple monitors, but run the game in full screen on a single monitor. In order to enable mouse grab after starting the game, I need to go into the options, disable fullscreen, enable mouse grab and just don't restart. I also re-enable fullscreen (also without restarting) otherwise the next time I restart the game it will appear windowed.
I have commented out the code stopping input grabbing in fullscreen mode and done some initial testing without any noticeable problems. I'll post if I come across any.