Possible Duplicate:
Windows 7 alt-tab window disappears to back when aero peek is enabled
I have a very annoying problem that appears randomly. Sometimes it works fine sometimes it doesn't. The problem is that the centered thumbnails that appears when alt + tab is pressed stays behind the window preview, so any subsequent press to tab it shows the full screen preview but the thumbnails remains behind it.
In essence, the z-order of the mini-previews is not the top-most. Any hint or way to fix it?