All cars which have canHideGunner=1 param in turret config cause driver (and only driver) unable to change seat.
In offroad case, FFV turrets have that option to turnout and prevents driver to change seat to i.e. passenger. While it's not super issue with this particularly car, it's very annoying for any modded vehicle.
Put unarmed offroad and try to change seat
isPersonTurret doesn't affect thing, it's solely canHideGunner param causing described issue.
if player will perform turn in action on all seats that have such option then it's possible once again to change seat as a driver
this issue also cause bad "camPos" reading -> try vehicle player getSoundController "camPos"; on offroad & switch between 1st & 3rd PP mode - script will return same values for both modes