My sister's RB meezer Poco also loved the bathroom. He had the same rule about the door. I think he also liked it because in winter, the bathroom was one of the warmest spots in the house because of where the heat vents were.
My sister reminded me that their first house had a pantry off the kitchen that had a door. There was a hook on the back of the door. If she closed the door to put something on the hook, and left it closed for more than a split second - the same rule applied, cat and person were not allowed to be on opposite sides of closed pantry door either.

What a great topic! kitties and bathrooms!