Random surname weirdness

[tangerine]

In my town, when two Sims get married I choose for them to live in the wife's house, which should result in the husband taking the wife's surname. I just had two Sims get married and he didn't take her name, but oddly he didn't keep his either. He wound up with a random last name (Green) that does exist in my town but is not associated with the house or these two Sims. (Although it is possible that at some point one of these Sims had been the roommate of someone with the surname Green, or a member of the Green family lived in this house; I just don't remember for sure. I've been playing for years and can't keep track of all the roommates, marriages, divorces and moves in my game.)

I was just going to have them divorce and then have her invite him to live with her and then get remarried but decided to give them a baby first but the baby has the father's incorrect surname. I'm guessing I'll need to do an ultimate makeover on the husband but I'm not sure that'll work. I've tried it before and it didn't work for one of the four household members; she was stuck with the original last name even after I tried having her move in with different Sims with different names. I had to recreate her to give her the correct surname.

Has anyone seen anything this funky before? Does anyone know what the surname rules are supposed to be? I thought the last name was tied to the house, which is why roommates have to have the same last name, but when someone new moved into an empty house, their last name became the default name for the house. Hmm, I wonder what would happen if I bought the family a dog. Which surname would he get? I'll test it just for fun.

[tangerine]

ETA: The puppy and kitten I just bought were both named Green. Strangely, when I pretend to move the family to a new house, the household is named after the wife; it's not called the Green Household.