Often when I'm using iTunes 10.4, the menubar will hide and show like the dock does when you set it that way. I don't know of any settings that allow for that to happen on the menubar. Is it a bug or a setting that I accidentaly changed?
If this is due to a setting or false install, try this:
Use an advanced cleaning to fully remove iTunes: AppCleaner http://freemacsoft.net/#
Then reinstall iTunes.
This will not delete your music, movies, apps! Only the program.