I've browsed the topics looking for a similar example, but I haven't found anything so far. Here are the details of the case:
In CAS, I created an ordinary male sim of medium complexion and outfitted him in ordinary modern clothes. He also got a teenage son. I placed them in a beach cottage in the Sunlit Tides neighborhood. It was a tiny one-bedroom place, so I had the dad sleeping in a bed on an upstairs semi-enclosed porch. There is also a large yellow Amazon bird residing on a bird tree on that porch.
I went to a different family for a few days and had this other female sim walk her dog to the dad's house and use the friendly greeting. She walked up to him, and he had changed to a coal black appearance, and he was wearing a frilly old-fashioned suit. She didn't notice, since she had never met him before, but I was astonished! I have Supernatural installed, but I use the options to have only fairies and horses active. But he doesn't look like any picture I have seen of vampires, zombies, werewolves, or witches. I looked through the scrapbook, but there was no memory of anything unusual. In the relationship panel, I saw that he dislikes the yellow Amazon bird (slider somewhat in the red zone.) His son seems to be afraid of him, but other sims carry on ordinary conversations. I had him take a shower before bed, and he briefly popped into his assigned outfit and complexion before instantly whipping into the frilly suit.
I'm playing on a Macbook Pro with all EPs available, but with Seasons and Showtime uninstalled due to problems I haven't yet learned to deal with. Also all SPs are installed except Katy Perry. And lots of stuff from the exchange on the EA website.
Sorry for the lengthy explanation of this curious case--any insight would be appreciated. Is it a game play detail that I hadn't encountered before, some technical problem, or just some weird thing?