I haven't downloaded the saber app, so that's definitely not the common denominator. Mine had an app screen underneath too, but I can't recall which one. It was a white background so maybe just email or something. I made the vid because I thought maybe this would be a virus or widespread problem, but apparently not.
Not too worried about it, I guess. Easy enough to get around with the home/wake buttons, and as far as I can tell there's nothing else that's going wrong. I'll assume it's a one-time fluke until I'm proven otherwise. An old boss of mine would've referred to this as "an FM not worth solving" (F---ing mystery).
-S