Probably the strangest thing which happened to me was in a trial run for the second baby boomer challenge. I demolished my house to create a bigger one for my enlarged family, however my sims kept interacting with the old, deleted furniture. I was laughing my head of as my sims began to get undressed and shower in imaginery showers, infront of the tv, go to the toilet on the floor, and take naps in midair!
I've never heard of this glitch happening to anyone else, and never had that problem with any other family, so I have no idea what happened!