It actually may be your hardware to some degree. It happens at different speeds between my two systems--an i7 laptop with an nVidia 670 series GPU and a C2D PC with an ATI 5800 series GPU.

I'm just glad it works without crashing the game... very uncharacteristic of SE to allow us to be able to alt-tab from their stuff without using a third-party tool. They're rendering methods in general are notorious for not getting along with anything that causes their game to loose focus.

We may not see any improvement until we move to a higher level of DirectX. Hopefully this will allow it to be more fully integrated with WDM (and finally resolve the hardware cursor issues Vista users are still having, among other longstanding issues).