Re: Workaround for mouse bug!
The mouse movement bug can be fixed while in game without deleting any files outside the game. The following is what I found corrected the issue.
In the Options menu click: Mouse & Keyboard, Vehicles, Key Bindings, Pilot, Movement. Use the (press and hold) ESC key to clear the "mouse bindings" for: Freelook UP, Freelook Down, Freelook Left, Freelook Right and leave them blank.
Then in the Options menu again click: Mouse & Keyboard, On Foot, Key Bindings, Movement. Use the (press and hold) ESC key to clear the "keyboard arrow bindings" (not mouse) for: Freelook UP, Freelook Down, Freelook Left, Freelook Right and leave them blank.
If you (previously attempted) to clear your freelook "mouse" settings for "on foot", you will need to rebind it even if it still shows in the box under mouse.