I teach, and I use keynote to show my classes the directions for the activity of the day. But with my MacBookAir, KeyNote will basically "hide' on me without warning, showing whatever is behind my Keynote. It does not minimize. It does not quit. To get back, I hit command-tab twice, which is not exactly what would happen if it were hiding, but hiding is the closest thing I can describe. Any ideas what is happening?