Only observed on a Barnes & Noble Nook HD, both Creative and Survival.

After returning from the Nook's lock screen, the screen appears stretched, and the touch areas for all the game's controls are shifted down about a button-height. After fumbling around a bit, and finding the Quit to Title button, the Minecraft logo is cut off at the top of the screen.

Exiting the game to the homescreen and returning resets the graphics to their correct proportions.

UPDATE: Note that the version and copyright messages appear in their normal positions on the title screen. This suggests to me that the game is receiving incorrect viewport dimensions from the operating system. If I had a test build/mode that showed the dimensions it's basing the screen size on, I could report back.