Minecraft wiki entry for Development_versions, associated text: Added camera controls.
These were accidentally added. Jeb noted them as "deadmau5 camera" controls and would likely be removed again in an upcoming snapshot.[10][11]
Pressing F6 causes the player to get "stuck" to the camera until F6 is pressed again. This allows players to appear to phase into blocks.
Pressing F9 causes the camera to freeze in its position, allowing to see the player model rotating in third person view.
Pressing Y, H, U, O, I, K, J, L, N and M change the camera positioning in a variety of ways. While pressing two functionally connected keys at the same time the camera may be reset (example: Y + H) will revert that view back to normal, but U + O will not).