Of and on it can happen that in an AI crew one will occupy the passenger seat instead of an important seat, like the gunner or driver seat.

So if you play as a default APC team consisting of you the player and 2 AI crewmen and let the AI disembark or switch to a new empty APC then one of them will sit in the passenger seat. Result is that you have to drive around with one crewmen that is not doing anything, while he should be (depending on where the player sits) fill up the driver/gunner/commander position.

There is also no command in arma to let them switch seat unfortunately, otherwise it would be no issue.

Yesterday I played a mission where they got back into the APC on the right spots just fine, today the gunner seat is constantly empty when you let them get back in the APC (panther in my case).