Wow! I had always just assumed it was a double-sided bar and there were two barmaids! I hadn't recognized it as involving reflections.
I remember being fascinated by mirrors when I was maybe three or four. I have a very clear memory of looking into one that hung on a hallway wall, looking into it at an angle and being amazed by how much imagery was in the reflection. I wondered how so much could fit into one piece of glass. It seemed magical.