The situation is this: you grab quests at say, level 14 and you run around and complete all the tasks they require. Run back to the NPC and you are unable to turn them in because they are quest lvl 15. I am only guessing at this, but I think this was done because you could technically level while doing the quest requirements, or grinding on your way there, or something so that when you get back to the NPC, you would have dinged 15 along the way. Then when you get back, you have a jump-start on lvl 15 xp. However, it is frustrating to be 3k away from 15 and have no quests left because you have completed them all and can't turn in any for that bump in xp that will give you that 3k. It is a very odd situation.