Pretty much every "long lunge" melee attack has hit reg issues. Destiny's engine doesn't seem like it's well equipped to handle that kind of player movement, at least when coming into contact with hostile entities. Swords, Grapple-Melees, Shoulder Charges, all of these kinds of moves seem to fail to register more often than they probably should. I don't suspect any fix will ever come. It's always been this way. The few times Bungie has posted saying that they "improved" hit registration, nothing feels any different.