wrong battle report

[Agrajag]

I don't think the difference here is a result of one spell having a different random outcome.

It's not the single outcome that changes that makes the difference, it's in how the game handles random rolls that causes a snowball type change.
Imagine that all random results are rolled in advance into an enormous queue, and then each time you need a random number, you get the first number in the queue.
If everything goes alright, then replaying the battle with the same queue will give you the same replay every time, because every result it predetermined; You will get the same "random" number for the same roll every time.
But if because of some small change, one less random number is needed than is supposed to be (for example, originally the mage casted a spell that also needs an MR check, but this time he didn't), then every single random outcome that follows is changed, because the random rolls will use a different number from the one they used originally.