Jon - With this moderated post approved your next and subsequent posts will be as a full fledged 'Bolter! No more waiting for approval! Congrats!
You previously mentioned "There's a lock inside the driver's door but not inside the passenger door.". Can you post pictures of both door innards so we can see what you do. It is possible someone replaced the keyed passenger door locking handle with a non-locking one. More to decipher when we can see some more pics.
