I'm suffering from random, sudden and unpredictable mouse acceleration. At some point when I'm turning around, my aim suddenly moves far far further than it was supposed to.
Game mode this occured in: Team Deathmatch
Maps: Stonehaven (was pretty bad, instead of looking slightly to the left I suddenly looked at my feet), gas station map (the one with strip bar, don't remember the name)
Time of incident: around 18:10 GMT +02:00 (Ukrainian time), 25.11.2013
Total number of occurences: over 10 in total on two maps. May have happened on other maps but not in such a severe way.
Reason behind this (likely):
FRAPS running at the same time as Steam Overlay, or mouse polling rate over 250 mhz (was 500).
I disabled FRAPS and reduced polling rate to 250 mhz and my problems disappeared - no sudden mouse acceleration any more.
Found a solution while writing a bug report hope it helps others!
Anytime you have multiple programs running at the same time, you run the risk of experiencing some hiccups during game play. I am glad to see that you were able to figure out that fraps was the cause of this.
I will continue to gather information regarding fraps and mouse acceleration, and escalate it accordingly.