^ LOL.. thats probrably because the party you are in is set to [exp auto share]
Theres two kinds of parties... the [exp] share ones have a limit of 4 people each, and give you 10% more exp when it is full, the [auto] share ones divides the exp you gain from killing a mob, and distributes it to the other (8)people in your party.
If you want to create a distribution party, press P on your keyboard in-game, then click [set party] > and check [exp distribution]
and no worries.. I didnt figure this out until lvl 2X.
