This might as well be the right place to ask. So I've had a few problems with my mouse. It's happened in at least two games so I'm guessing it's the mouse itself at fault. It's a Razor Copperhead. What happens is I'll be playing a game and gradually I'll notice the sensitivity drop. I like the mouse to be nice and sensitive, and I really notice it when it slows down. Eventually it becomes unplayable, as in you need to frantically flail about with the mouse just to get the cursor to cross the screen. Exiting the game doesn't solve anything once it's happened; I have to restart my PC to fix it (the slowdown carries on even just browsing windows unless I restart).
But this doesn't happen all the time, and only certain games seem to be affected. I've figured out that it happens whenever the RMB is held down while the mouse is moved heavily. The two games I've noticed it happening are DDO and Skyrim. In DDO, particularly as a melee, you're holding the RMB a lot as it's the main attack button and you're often strafing around enemies. In Skyrim it only really happens using the Bow, and particularly fighting dragons; if you're holding RMB to keep the bow drawn and you keep the cursor over a dragon that's flying over your head you have to turn quickly and it never fails to cause this problem.
So is this likely to be a mechanical fault or is there some special hidden checkbox somewhere that says "do you wish to prevent that fucking annoying slowdown thing?" that I'm supposed to have checked?