I finished a quest for an exotic cipher from Xur. I did not realize I could only have 1 in my inventory at a time. When going to finish the quest by talking to Xur, the game mentions that he gives a gift, but nothing actually pops up. My inventory still just has the one exotic cipher I had previously. So, it seems the game does not block you from finishing the quest to prevent this issue. It lets you turn it in and just kind of never gives you the exotic cipher you just earned. It's not in my mailbox, and there's no where else it could have gone. I see that others have had this same issue, but I did not see a bug report for it. I really hope this can be fixed. It is really annoying if I actually lost it.