Today I hired two level 10 dwarven priests (to go along my pre-existing maxed guy) with anticipation of doing the dwarf priest only level 14 quest. First I had one of my warriors take them through a regular level 10 adventure (Viscous Tombs) and they both appropriately got 10 xp for their contribution. Next I went to the level 11 Pools of Slime. After completion, my first dwarf got 15 xp and dinged 11, while the second guy only got 5 and remains level 10. Logging out and back in made no difference.
That . . . should be impossible. And if they're both new level 10 hires, then the only thing I can imagine would be that you DIDN'T set them adventuring at the same time, and thus only one of them did the Viscous Tombs. But I think you'd remember something that obvious. Anyone have any other ideas?
I suppose its possible that the bug occurred after the first adventure (where dwarf #2 got nothing) and I failed to notice, but no way was either dwarf treated differently. My disappointment was tempered by St. Olf's Fiery Pike in the final chest.
While it is of course possible that this was a bug, I would put my money on a simple human error, because what you describe is exactly what happens when one character is higher level than the other. I've experienced some "XP bugs" myself, all of which turned out to be false. You do know that high level characters get downgraded to the appropriate level, right? If you didn't know that, maybe it could be the reason for this whole situation. I think that at some point you used some other character that you thought was the newly bought dwarf priest.