Troublesome lock

This is part of a lock on our ancient garage/shed/junk repository.

The only way to lock the door is to insert the key on the inside (with the door open), then turn the key as if locking the door. With the lock tongue extended, withdraw the key and insert it in the lock on the outside (this view). Slowly turn the key as if unlocking the mechanism and when almost all withdrawn, close the door and turn the key to lock the door.

Voilà, a locked door!