My doors are the same -- if you lock 'em from the inside, you can't UNlock 'em from the outside. That's because the key-locks simply prevent the knob from operating, whereas the inside lock (pushing the door handle) does a completely different deal.
The door knobby-thing pushes against a tab (inside the door) ... if the knobby-thingy-deal is worn, I would BEND the TAB that it pushes, so it's closer the the knobby-whatchamacallit-thing.
LOL! I'm a great communicator, ain't I?