I have also witnessed this flickering.
Specifically, I have noticed the flickering in IO radioboxes and checkbox controls. It doesn't matter whether I mouseover the text portion, or the 'actual' control area, the control in question (text and control) flickers slightly.
It's not a big deal at all, which is why I haven't mentioned it.
I'm using a daily snapshot from April 14th, on XP pro (no Service packs, cleartype enabled). (By the way, disabling cleartype doesn't make the flickering go away.)
I do not notice any flickering when mousing over radiobox or checkbox controls in other applications...
Like I said, not a big deal, just wanted to confirmCodeSquid's observation.