Here's an update to this recurring problem which may be helpful! I recently returned to AHII after a long absence with a new computer and flight controllers all of which required going through the arduous task of mapping them to my liking. During that process, I too experienced a lockup of the keys which control head position.
I found this thread and renamed my settings file which helped temporarily. Turns out, the actual problem however was related to my efforts to program my mouse controller to point and fire guns in bombers. For some reason, mapping the mouse keys would lockup the head positioning keys. When I unmapped the mouse keys, I would get my head positioning capability back.
The trade-off is I can't use my mouse to control my bomber guns. Any thoughts?
ez