Recently encountered this bug in my latest playthrough. If you kill the Rathound king before completing the Burrower Emergency quest and go to turn in the quest, there is special dialogue when speaking to Edgar mentioning that you already met and killed the Rathound King. When the quest is completed in this manner, you are awarded he money and the option to gain the hunter feat, but do not receive the 3500 Exp you would when completing the quest normally. This bug happened for me on the classic exp system.
