I'm not sure if this was always the case, since I started playing vanilla WoW around the time Nax was released. but during that time and definitely from then on, EVERY time a friendly NPC was killed by an opposing faction player, an alert was sent in the channel. I very rarely see pings in the world defense channel, it seems entirely unreliable. This takes a lot of fun out of the game because one of my favorite things in vanilla WoW was responding to pings in the world defense channel.
Is this working as intended or a known issue? I haven't seen a post about it.