Strange stuttering due to input

Very strange. I have an Athlon XP 3500+ on a MSI mobo with VIA K8T800 Pro chipset, an AGP8X GeForce 6800, and 1 GB Kingstom ValueRAM (CL3) in dual-channel mode. Not overclocking anything. Very low temps and no thermal problems. Optimized configuration. No malware. No system tray bullshit.

Everything ran fine, until it suddenly didn't :) , although I hadn't installed anything that day. After exiting a game (Morrowind) and restarting it later, now I find input stutters when it's going too fast. Notice I said input, as the game reports it's going at a rock solid, limited 85 fps, and if you're on autorun, or moving with keys, for example, it's indeed smooth. Problem is, input is stuttering. You have to move the mouse a lot to get any reaction, and when you do, the camera jumps quite a bit in every step (yet it's going at 85 fps and I can see it if I move with the keyboard). Keystrokes are ignored half of the time, as if it were losing messages. When the system is under some load, i.e. the game slows down to under 30 fps, it's back to normal, although the mouse movement lags a bit. Everything else works fine.

I'll try updating chipset and graphics drivers, and toying with some options, although this was working yesterday without a problem, and I didn't update anything. In the mean time, if Anonymous knows exactly why is this happening, I'd be glad to read about it, thanks.

Wait, I think it's a problem with the game (Morrowind). And a very strange one, considering I haven't changed its state. The game's event handler misses more and more messages the more idle it is (since it's limiting FPS to 85). In other areas, like a house, and facing a simple wall, it'll miss 95% of them, to the point I can no longer turn with the mouse. Keys are missed too - except arrow keys (whatever they're set to) which always works, that's making me think it's a problem with the game. And a strange one.

Fixed it. Turns out it was a rare game bug that didn't manifest with older computers. It seems I did change something - I set the music slider to the minimum. When you do this, the game attempts to optimize it by disabling music (as it should), but there's some bug: in one of the game loops, and one that's not in sync with fps, the game seems to check for something and post an event to its process event queue. On very fast, idle CPUs, it'll overflow the event queue and lose events. The less CPU time taken for rendering, the more it'd flood it. The solution is to set music to just one bit above zero.