My friend and his wife have this strange issue with their iPhone 5 (Sprint) keyboard. Whenever it prompts him to enter his password for iTunes or for the App Store, the keyboard looks glitchy and strange as shown in the video here:
My wife and I haven't seen this issue on our iPhone 5's yet. Apparently, this guy had the same problem on his Sprint iPhone 5, and someone at the genius bar told him to reinstall iOS 6, which apparently fixed the problem. I wonder if it's isolated to Sprint.