I put some vampire armor in her inventory at one point in Shriekwind Bastion, and removed it later for selling. Afterward, I fast traveled to Windhelm to make and enchant a dwemer battle axe. When I entered Dragon's Reach, she was wearing the vampire armor that I had already removed from her inventory. So I removed it. After fast traveling, she equips vampire armor that I have removed from her inventory repeatedly (to test it). This seems to mostly happen during fast travel, but it is a bit frustrating since I have equipped her with exquisite dwarven armor, which makes her a fairly reasonable tank.

I tried to search to see if anyone else has had this problem and I couldn't find anything. Any ideas?