Hey TaylorR,
I was asking about the mouse loop, not the keyboard loop. What happens on my machine is (with setGrabbed(true)):
a) when moving the mouse around, without holding any key on the keyboard, I get 1 mouse event per frame.
b) when moving the mouse around, while holding any key on the keyboard, I get 2 mouse events per frame. One of the two has tiny dx/dy.
c) with high DPI settings, it becomes horrible (sometimes I get dx values > 5000).
But that's on Windows 8.1. If this is different from Windows 7, then the workaround I had in mind won't work. That's why it'd be useful if you could post the exact code you're using and the behavior you're seeing. It's also not exactly clear if what you're seeing is rendering stuttering, or simply the dx/dy values are wrong and cause your animations to stutter.
If you don't have time to write a demo, you could do the following: Disable mouse grabbing, move your mouse slowly from left to right and print the dx values you're getting. Then do the same with mouse grabbing enabled and attach both results in a reply here.