It does need fixed. I've not sure if it's an issue with negative accel but it's inconsistant for me when looking around.
I can move my mouse the exact same distance horizontally across my mat but depending on the speed I move it, it will turn my soldier a different amount each time.
Try the solution I posted on the previous page.
http://forums.overclockers.co.uk/showpost.php?p=20397091&postcount=30298