I have the same problem. I really just think its my video card being too old.
It's extra annoying for me because I can't see the ground either so I have to use the mini map to move. To stop i usually just load windmill.
i don't know if it's the same thing, but when i hold down certain mouse buttons, for example left mouse button, i sometimes get a momentary lag spike and when i get out of it the mouse is stuck clicking, causing me to move involuntarily. clicking again stops the problem though. same goes for right click, it will get stuck in that POV rotation thing.