I did my hunters bounty first and got a key, then I did it on my warlock and didn't. My warlock happend to have a key in his inventory when turning in the bounty so I wondered if that anything to do with it. Then I made sure no keys were on my titan when I turned in his bounty and got a key. Hope this helps. Edit: This was only on the first wanted bounty per character. idk if you can do it again if you didn't get a key the fist time. I'll try it again on my warlock and update my post when I do. Edit 2: I just realized that my warlock had some wanted bounties from last week and I turned some of those in along with a new one. This might have been the problem especially if I turned in an old bounty first. My titan had some old bounties too, but I dismantled them all before I even picked up the new ones.