You can eliminate iOS7 as the problem. I have had this happen on two or three occasions and I have yet to update to iOS7. Unfortunately, I can't recall what was going on at the time, so can't help with the troubleshooting. Interestingly, this last weekend, while docked and playing music, the iPad strip meters were absent. Stopped the music player, undocked and redocked and all was good. Only time that has ever happened.