NEW JUNE 2013 BETA:
http://www.youtube.com/watch?v=mqWUpYQbX68&feature=youtu.be (25 secs)
http://www.youtube.com/watch?v=JbLpv2-CY8c&feature=youtu.be (15 secs)
Issue unexpectedly happened again just as described before.
In the second video I quit to the menu and much to my surprise the issue persisted and appears to be related to mouse movement rather than turning and rendering which was my original assumption!
Seems like a very rare issue regardless and is solved by restarting the game entirely.
In 100 hours of gameplay I have only had it happen a total of 3 times.