The Mystery of the Opening Door

I solved the mystery of the opening door. Every night we lock our cats on the living room side of the house. Princess was *not* opening the door with the doorknob, as my mother suspected. She was just putting her weight on it, and it was opening. I thought maybe the door striker needed to come out more, so I adjusted it with some washers first. That had no affect. Then I came up with the brilliant idea to switch the whole door knob and lock mechanism with the closet door in the hallway. After replacing it, I was shocked to see that even then it would swing right open. It just was not clicking shut. So, finally I determined that the door itself was coming down too far, and it was therefore missing the lock opening (on the door jamb). It probably needs to be raised about a quarter of an inch. How it came down so much, I don't know. I tightened the hinges down, but that did not help. Anyway, at least now I know that after I close the door, I have to lift it
slightly so that it will lock in place; then, the cats cannot just push the door open. This is dangerous if they venture into the hallway at night, because when any of us step out of our bedrooms, we can accidentally step on them. Two nights ago my sister stepped on Nikki's tail. She just was not expecting him to be in the hallway.