So I've encountered this more than once. I had 10 bounties to turn in. Some for crucible and a few vanguard ones. 5 of them were 5k xp bounties, 3 were 3.75k xp and the other 2 were 2.5k xp. I had my hawkmoon levelled up to the point where it had just gone past the first upgrade which is the first lucky bullet one. Handed in 10 bounties, next thing I look, it hasn't even brought it halfway through the first damage upgrade. This has happened to me with universal remote as well. I don't know if it's a glitch or a bounty bug, but I've handed in less bounties and gotten more out of them on exotics before, and it's very frustrating when you spend a good 2 hours playing to get those bounties.