1. Get in vehicle with gun for pilot e.g. AH-9, WY-55 or jet
2. Freelook away from the center of the screen
3. Notice how the crosshair deviates slightly from the center of the screen in the direction of which you first freelooked.
4. Repeated attempts to freelook will not do anything - it only occurs on the first time you freelook.
Edit: This occurs to a greater extent if you hold "Ctrl" (to move your head), causing the crosshair to deviate so far that is was off the screen for me. Is there a centre option, to re-centre your head after moving it?