DrewYou mean a lot really shitty mouses do that.
You'd be surprised about how very few good mice there is (mostly the sensor's fault). Here is a link for you because I don't feel like explaining everything :
http://www.esreality.com/index.php?a=post&id=2024663
To make a lil tldr though : Lot's of mice have innate issues or they start to malfunction at a certain speed
malso if you want 1:1 mouse movement please dont ever move your windows slider off
With m_rawinput 1 that's irrelevant because it bypasses your windows mouse settings