Having leveled manually from 1-60 on my 4 shaman teams I've noticed this twice in all my turn ins, and I dinged twice by turn in for every time I dinged by kill XP.

For a LONG time the two vet accounts were 1 300% quest behind.... then around 40 it flipped and the vet accounts were ahead...

One thing I did notice, and correct me if I'm wrong... but when the accounts were different levels, they both would get 300% xp for kills and quests even though the higher level shouldn't have...