Sure he did!
The mouse doesn't work properly.
</sarcasm>
Since the issue you're having is in newer clients (TF, GPP) try this if you're on Linux:
export SDL_VIDEO_X11_DGAMOUSE=0
Otherwise, like David said, we'll need more information to give you a hand with your issue.
What does that actually do?
Anyways, loki, what kinda bug is it? You need to be more informative.
Some bugs i encounter:
When i try shooter games on my mac through a virtual machine version of windows, the mouse turns into a joystick that only moves when you move ur mouse.
Also, on gpp, the 'actual' sensitivity is lower than 1.1. [for me. It may be because gpp may ignore the windows sensitivity, not sure]