As the topic says, i am sure the problem is with mouse, but probably not hardware wise(i dont have any issues with it so far in windows or other games). When i press mouse2 (i use it for jumping so its pretty crucial), sometimes paintball wont react on button press but only after i release it.
I installed latest drivers for my mouse, tried [X] Raw input checkbox (no idea what that does, just felt like it could help ^^). Also tried using diferent USB slot.