Connect to a UAV that allows freelook in ViewPilot or has turret.
Bend your soldier up/down
Take UAV controls/turret controls.
Look into a certain direction(HPB).
Disconnect from UAV while still holding down the Alt-Key.
Experience weird incorrect head angles (tilting, gimbaling).

This is a very, very minor issue, though it still is an issue.
edit:
As reproducing the issue, it came out, that the strength of the effect is varying. Couldn't reproduce consistent behaviour.
However, the example video provided shows a slight tilting. I recently experienced this effect much stronger. Will upload another video if I am able to reproduce the issue with maximum effect.

edit#2: It turned out that the view angle after releasing UAV controls is strongly related to the initial view angle of the player. See 2nd video attached. If one starts walking, angles will be reset (not fully on releasing Alt-Key).

edit#3: Attached mission & another video.

ViewPilot Settings in config.cpp:

		class ViewPilot : ViewPilot 
		{
			initFov = 1.1;
			minFov = 0.6;
			maxFov = 1.7;
			minAngleX = -75;
			maxAngleX = 15;
			minAngleY = -140;
			maxAngleY = 140;
		};

Video: https://www.youtube.com/watch?v=E9XOxgIx2aA
Video with clearly visible effect: https://www.youtube.com/watch?v=VwmtfjhDhWw
Video with darter: https://www.youtube.com/watch?v=ajT44zIkmDw