Which mouse are you using? Any special drivers?
Hmmm, it almost sounds different
endian to me. Or a bit is stuck on on both axes. Up and right are negative numbers. Examlple: one axis 8 bit binary is stuck like this: xx1x xxxx. This doesn't effect negative numbers (-1 = 1111 1111, -2 = 1111 1110, ect), but will effect postive numbers (instead of 0000 0001 for one, 0010 0001 or 33). But for both axes is very unlikely.
Related, but a little different. I have (in storage) a mouse with a scrollball (like a scroll whell, but a mini trackball). If the driver isn't installed, the mouse works fine, including the up and down scroll. Side to side scroll, OTOH, is seen by windows as super fast up and down scrolling. That's because the sideways just used the upper bits of what normally is the up-down scroll wheel.