I notice when switching between 10.1 release and 10.1 stable that mouse sensitivity (for small movements) has changed somehow. I think the acceleration for small movements is now too fast / non-existent. stable/10 - r281836 I have a G400s mouse with a high dpi. Please let me know what information I can provide to give better debug output.
Closing this. This was totally hardware related. The + and - on the G400S toggle the speed / sensitivity was the issue. I used another usb mouse and fixed the button in the G400s and both work as intended.