Initially, that was the case with Soul Shards mobs, they would de-spawn after you exceeded the 16 + block distance from them, like Vanilla mobs, but Eloraam requested they don't de-spawn so automatic mob farms could function with the user away, provided the chunks were loaded in the first place. Shadow Dragon made the change, but I must confess, I found the mobs de-spawning regardless. Granted, it only happened when there were excessive amounts of that mob in a fairly small area (we were having problems trying to turn the spawner off, someone on the server neglected to make a wireless redstone transmitter to change its state more easily), but we found that once anyone nearby the spawner logged off, the mobs de-spawned.[DOUBLEPOST=1362069760][/DOUBLEPOST]Rethinking my post, I remember the area chunkloaded via spot loader for that spawner we had was off to the side for the portal-gun portal, (we were experimenting with stopping us from getting trapped in the blocks.), so the mobs de-spawning might have been because the contained area they were trapped in when we disconnected wasn't loaded.