here's what happened to me...
I used Heart of Shao-Lau early in the game, and since it has a cooldown of 3 turns, I'll have to wait for another couple of turns before I could use it again. In the second turn (in-between the cooldown time), Arcade stunned my characters, and because HA Iron Fist doesn't enter the "stunned phase", the game was stuck with him (see visual description above).
And I want to know if it had happen in another scenario outside of SpecOps, please inform me if it does. If no one ever tried it outside of SpecOps 15 yet, then I guess I'll try it myself for a while (though I guess it might take long).
Anyway, I'm just sharing what I found out! Be careful! ^_^