Slaver King Vigilante contract not awarding Tibbs experience

I've run it with him about five times, at level 80, killed Tarollo each time, left the instance and he gains no experience. I notice that no portal spawns to leave from the bone pit, but I don't know if that's meaningful.
I'm going to run it with Huck now. I'll post if anything different happens.

No different. I ran it again with Tibbs to be sure. Both times I get "Contract Complete" on the screen, no portal, and when I finally exit I get no contract completion experience for Gil Tibbs.