Yeah been that way since day one. Never been said to be a bug, but it exploits the physics engine to cause the kill damage. On hit it give you a velocity high enough to kill on contact with a surface. Given its a slam and you're already on the ground, instant death. You can do the same thing with a lunge player melee. Stand just with in melee range and let the game lock it on for you. Next have someone run between you and target right when the lunge starts. You smack into the non target without hitting it with your melee and launch them a good ways. If a wall is near, sometimes it can kill. It's either a glitch or creative programming by Bungie to avoid coding a real melee attack with set damage.