This is one I've never seen before that just cropped up a couple of days ago. The MBP will be running then at some point whatever app is on top stays on top. For example, Safari is running and I click on Mail, but next to the apple icon in the upper left corner it still says Safari and the Safari window stays on top of all others. If I minimize Safari into the dock and click on another app (Mail, Finder, whatever) that window comes to the top but it still says Safari by the apple. So then I quit Safari and whatever app name appears next to the apple starts the cycle all over again, remaining on top unless minimize. Quit that one, and whatever app is next has the same problem. The only solution is to restart the MBP. But after a couple of days the behavior returns. Anyone else experience this problem? And I have to say, I've been using Macs since 1992 and Mountain Lion is one of the worst OSes Apple has produced. I have had more problems with it than any other OS.