Yeah, I have had the same problem since the beginning of my game. It looks like auto_resolve only works with sword play and not magic.
I found out that even with a sword if I do auto_resolve it is pretty much a tossup if I will win unless the guy is really weak.
Yet, my same guy can use magic and break down swarms of armies with the current magic bugs
For example.. confusion takes their attack to negative (-) levels and then they can't fight back 
