Huge flicker when raising windows?

[John Firebaugh]

For about a week with latest CVS, I sometimes see a large amount of flickering 
when raising windows, as if a second, lower window is being raised and 
immediately lowered before the proper one is raised. This seems to happen 
mostly when Alt-Tabbing between windows, and appears on two separate 
computers. It's very distracting. Does anyone else see this?

-John