Head tracking mode is a modification to the interface to make it easier to use with peripherals that allow for in-game head movement, like TrackIR. It can be activated by using the keybind U
Head Tracking Mode unlocks the central cursor (
) so that it can be moved around the screen using the mouse.
The central cursor will reset it self back to center when disabled
If you wish to disable this feature for head tracking mode, then it can either unbind the the action or set the sensitivity to zero