That quest is definitely bugged, the idea is that you can only do it once.
I rolled back the Mercia reputation to the values of the first time they were completed, because having them set to 100 so quickly will spoil some of the future content. I forgot about the Jabal one. But I will not rollback any of the XP or gold.
If you want to do it the way it was designed, you have quests in the town halls, you can do those and earn a lot of reputation, XP and gold with an edequate challenge.