I am unsure why this is happening, but the mouse movement is rather jerky ever since i got windows 8.1 (insert "There's your problem"). Not in that the framerate looks low when moving the mouse, it looks smooth, but the way the camera moves in jerky and looks like it keeps speeding up and then slowing down...it is hard to explain.

Is this an issue with windows 8.1? This never happened when i had windows 7.

I think this was some general issue with games and win8 - try to googling "windows 8 mouse lag games".

This doesn't affect other games however.