I've noticed the same occurrence a couple times with different groups.
I had been speculating that it might have been due to a quest that was green before a turn in, and then became trivial after the first to completes it and levels.

Though now that that I look back it does seem like every time it happened if I turned in the quest with the veteran account first. I did manually catch up one of the shaman since it bit me on a 30k reward and that much of a disparity was bugging me.

-Stav