Wonky Auto-Resolve? Might just be underground battles?

I've had some odd auto resolve results and I was wondering if anyone else had the same. I had a stack vs stack underground battle that the auto resolve had me at around 90% balance of power. I played it anyway, since I just got my dwarf army some new toys, and got destroyed. I reloaded and the autoresolve won me the battle with only a hundred losses.

At first I figured I just got cocky/played poorly/not use to playing a ranged weapon heavy army, but when I jumped back into the battle for round 2 and paid more attention, I realized that that couldn't explain the big difference - the other army had about 8 units of black orcs who tore through my lines.

Another battle later (also underground) went the other way - auto resolve said I was doomed, but the battle itself was quite easy. Their force had Grimgor who was a bit of a problem, but besides him nothing but trolls and goblin skirmishers who were easy pickins' for my army.

This was the same army I used too. I think either autoresolve is bugged for underground battles, or it has really weird interactions with artillery-heavy lineups.