Checked my video card drivers
as well as the Desktop Window Manager. Video card up to date, DWM working properly.
It's so strange, I may have done a bad job explaining the problem because it looks like it works but then something else is happening to close out of the preview or the alt tab or tooltip. If I keep moving my mouse back and forth on the same taskbar icon the preview keeps flashing on and off really really quickly!
I wonder if some registry value didn't get changed or something. Perhaps the time that the preview is supposed to stay visible before minimizing again. But if that were they case then a system restore should have fixed the problem.