Why do my creatures randomly cast Inner Destruction

[phadin]

I've been struggling with this for a while, but now I'm in the boss fight at the end of the torture realm, and even as I sit there defending constantly, my creatures randomly just kill themselves with Inner Destruction. I have no idea how or why this happens to my creatures. Can someone explain this to me?

[Starsinger]

Inner Destruction is a chaos spell gem that is really popular with the AI. When it's equipped, the opposing team has a 20% chance to cast it at the start of their turn.