Since the 3.0.59xx version I downloaded about 2-4 weeks ago (apr. 16th or maybe apr. 8th, I'm not sure about that but probably it's somewhere in between 3.0.5950 and 3.0.5941), MB suffers sometimes from GUI corruption at the top and the bottom (app. 70 pixels high, full screen width). This happens after I switch to MB (it's already open). In those areas the content of the program I was switching from, shows up in MB (hope I can make myself clear; English is not my native language).
E.g.: I'm in Firefox. I switch to MB (ALT TAB or whatever method) and then I see parts of Firefox in those top and bottom areas.
NOTES: No changes to my PC (same drivers etc.). It's not dependat of the program I'm switching from. Happens about once or twice a day. ALT TABBING a few times does NOT fix it but minimizing and restoring DOES!