'85 300CD-T Passenger Door Lock + Alarm

My new (to me) '85 300CD-T has the factory installed alarm.

The master key for the car (square headed) will lock/unlock door & enable/disable alarm for the driver's side of the car just fine. On the passenger side, the same key will only enable/disable the alarm - it will not actually lock or unlock the door. Is this the way this is supposed to work? My '83 300CD-T doesn't have the factory alarm and the master key will lock/unlock anything on the car with a lock.

Perhaps the door handle/lock on the passenger door of the '85 has reached its limit of wear?

Any clarification/help appreciated. Thanks-

Terry