Hrmm... my problem is if I have my own horse, when i kill an enemy, regardless of whether the horse dies or not, it just disappears, and it's not in loot, unless I dismount my horse, and then kill the guy.
I just now killed 2 Forest Bandits on horseback, the bandits' horses were still alive, but I was on horseback also. The horses disappeared standing up, and the only loot I got, from 11 forest bandits, was some bent arrows... no horses.