This is a bug that is almost sure to be fixed before the patch goes live, of course, and with good reason. It'd be a bit of a drag if life for the Shattered Sun Offensive was a constant stream of fighting off massively powerful pit lords unleashed by a stream of bored warlocks. But still, for one brief, shining moment, all you Demonologists can bask in the glow of true power, and know that you once caused one of the mightiest of the Burning Legion to bend to your whim. Yeah, that's right, it's good to be the Warlock. And your parents said studying the dark arts would never get you anywhere.
Thanks for the tip and the screen shots, Pamine!