honestly, I think its just dark, nonreflective surfaces it sruggles with, then adjusts after a few seconds. Often I find on my black mouse pad that my y axis stops responding out of nowhere, after moving my finger over it, or puting it on the bare table it starts going again. Recently, I got a teal blue mousepad made of the same exact material, and never have issues. This isnt saying you arnt having a differant problem, but it seems similer to a problem I found a solution to.
On another note, My R.A.T. 9 dpi rocker is way too sensitive on the forward side. IT clicks when i push on the back, but it makes no click forward, and reacts on a hair trigger, making it difficult to scroll through weapons and accidently brushing it. I have put up with it since opening the box, and i rarely hit it anymore, but im wondering if this is a malfunction of somekind, like +dpi should have a click or something. :S