The lock and the keys

Our Fuda key was not working very well; it was very hard to turn the key from the inside. And it's just not one key, a few keys have been "broken" after they were dropped a few times to the floor. I told my father that this particular key shape was probably less resistant to being dropped, and we should probably just change the door lock instead of buying the same key again and again.

My father: *Fiddles with the door lock until the key can turn, then shows us that every key, including the older "broken" ones, can be used* See, it works now!
Me: You need to try turning it from the outside too!
My mother: The door is open now, you need to try turning the key with the door closed.

Did we miss any use-case scenarios? :P