This happens to me all the time. I shoot someone with a shotgun (or melee), they keep walking, kill me, and then die (and in some cases, I get a Postmortem medal!). My internet connection is very fast and I don't have any issues with any other game (or even with other game modes in Destiny). Also, another thing that happens less often, I shoot someone several times (sometimes together with another teammate) and they don't take any damage at all and then kill me. Is anybody else experiencing these issues?