Yup I had the same problem, I killed all the units except the super powerful archers, that devastated most of my party without me being able to touch them (I had 6 low level units + a summoned bear).  It seemed hopeless for me to win, since I could not get close to the archers.  The group of Brigands is very overpowered for the early part of the game.  2 of them have 2.5x (21 hit points) the hits of my most powerful unit.  Anyhow I hit the autoresolve button after realizing it was hopeless, and I won!  Woohoo! Sort of......There would have been no way for me to kill these units, I was totally out of mana! I ran away from the main group of brigands, sent the bear in to combat directly, it killed all but the two archers before it died.  I tried casting fireball on the archers, and got zero damage on 3 tries ???  Anyhow something wrong with the autoresolve, and something wrong with having such powerful units so close to my main city so early in the game. 

http://dl.dropbox.com/u/9594297/Elemental%20Debug%20text%20file.txt

The autoresolve seems to calculate combat very differently indeed. I met a single darkling (those 5 health 1 damage things), and autoresolved. Sovereign dead. I had some 13 health and 6 attack, I think. Then I loaded autosave and killed it on manual.. I could've just clicked next turn and won. I suppose it's possible to lose, but very unlikely. Similar things happened a few times earlier.

Also, autoresolve doesn't seem to use spells at all?