That does sound like a glitch of some kind. I have several two story homes in my saves and I have never had any Sims dress in cold weather clothing before going downstairs. I have a mod that forces my Sims to change into regular clothing after coming in out of the cold. It's quite handy. But to address your problem, have you tried to delete your caches then repair your game yet? Deleting the localthumbcache then repairing your game after installing new packs, updates or patches is very important. Allowing that thumbcache to grow each time you play and not deleting it afterward, will cause glitches in your game. The repair option that Origin implemented for Sims4 was the best thing they ever did for the game. It has helped me out a lot over the years.