Camera rotates around character. Game does not respond to any input, including opening inventory, pressing the "Alt" button, changing perspective (1st/3rd person), opening the options menu with "Esc" and so on. Needed to force the game to quit. Upon reconnecting to the server, normal functionality was restored.

I have not been able to reproduce the bug, but I believe it may be more likely when sprinting, due to the requirement for more textures to be loaded.