I posted this as a bug, but I figured some other testers might want to know:

After reaching the end of another game, I started auto-resolving battles, but was still amazed at how much mana the AI wastes - curious, I checked the details screen, and noticed that the spells cast didn't seem to add up to the enormous amount of mana drained.

Adding it up by hand in a manual battle afterwards, I realized the only way it could be using that much mana is if the spells were cast at full cost - and my mage hero can cast all her spells for 1-2 mana soooooo.

Anyway, just something you should be aware of if you're auto-resolving battles - until they add in controls to disable autoresolve casting or set a cap on mana spent, you're going to drain wayyyyy more mana with auto-resolve than you should be.