My companions keep changing their armor (Warband 1257AD)

I have my three companions outfitted with great gear, but after every siege or battle that I personally participate in they're suddenly wearing linen clothes and riding level 1 horses. One of them even had African hands instead of the mail mittens I assigned them. Their other armor disappears, so I have to keep buying new armor.

Anyone know what could be causing this? I'm abandoning the loot after every battle.