Yep, I was using a full bedroom set... Denise, Vivian, Adanne, and Leah. It was streamlined mode, no saves involved, don't remember which order. I'll run test tonight and see if I can get it to happen again. I tried to get to to work at the beach with Crystal and Rosie, but they seemed to work fine.
Viewing post in Bug Report... Denise has a twin sister...
You might have hit a fluke where the finale was turned on right as the composite image was in the middle of being built. That should be exceedingly rare though, hard to make happen even on purpose, and probably not worth fixing. If you can reproduce it multiple times, then something else might be going on I didn't think of.