Might be a glitch but Mjoll the lioness, my wife, will no longer wear clothes no matter what's in her inventory. I blame Aerin, as I've spotted him leaving my whiterun house numerous times. I dealt with him.
It's a stupid bug that needs to be fixed, several people have experienced it. Aerin seems to be glued to Mjoll whenever she isn't a follower. The only solution is to kill him unfortunately, shame really he isn't a bad person ... just a serial stalker.
If you think it's a bug post it in the appropriate forum.
I didn't spend enough time messing around and waiting in game to determine if it's a permanent problem or if it will fix itself over time. Mainly make the topic to show off the weirdness of it happening.
.....and my subtle reaction
EDIT: But I do know that it's not the same case of higher armor rating in inventory confusion that people have.
Wow just how sad can a person be having an NPC replace you in bed with your wife. Good Job offing him. I think you still have unfinished business with "The Wife"