It's not a question, but an experience... I spent a day to figured out this problem.
Situation:
An AI group get in a truck and travel to somewhere and get out and then they take gunner positions in fixed cannons.
Problem:
They never take the gunner position with AssignAsGunner and OrderGetIn.
They left the cannon inmediately if MoveInGunner.
UnassignVehicle is useless.
Solution:
Somehow (ArmA engine) they got an "AllowGetIn false" command when thet get out from the truck...
So after assignAsGunner, you have to "allowGetIn true" and then orderGetIn...