At around 12:00 server, I was in a 5 man group for this quest. It was going fine until the second ambush of elites occurred at the entrance to Blackrock Mountain (Burning Steppes side). Grark Lorkrub ended up just sitting there as we killed the mobs. I think one of the elite dragonkin mobs despawned for some reason, and two of the Blackrock Ambushers did not engage us until we attacked them. However, the second dragonkin mob did attack us as he was supposed to.
After we cleared the pack, Grark Lorkrub kept standing there, doing absolutely nothing. We tried:
1) Dragging a mob on top of him.
2) Abandoning the quest to see if he'd offer it again.
3) Use our Thorium Shackles on him.
4) Going back to his spawn point.
5) Opened a ticket and waited for a bit until people gave up and went to bed.
This is where the bug gets worse. At his spawn point in the fortress, he did not come back long after his 15-minute respawn is up. Unless a GM already removed him from Blackrock Mountain, then he's probably still there as I type this.
This is a very frustrating bug, as it cost me and 3 other people a quest that it's nearly impossible to find a group for, has a ton of elites, and has a good reward.