I have been seeing this issue more and more often. Sometimes half-size. Sometimes quarter or eighth size. Not the whole UI, just the video playback. Delete/reboot/reinstall did not help.
What works for me is to hit the back arrow until you get past the close-this-app prompt, and then relaunch the app. The home button doesn't have the same effect. ***Close the app.***
This seems to happen when I hit the back arrow to stop watching an episode of a series, but leave the device at the series screen. Once it goes to sleep, it wakes up in an odd state.
Possibly related, I believe when it's in this state, launching the app from the home screen doesn't prompt me to select a user. (Not a big deal for me, but I could see how others might care.)
