Is this using S6Ep3 files? I've had a Death King spawn in my PvP area (not a duel ring) in Lorencia also, and its not an actual spawn in the files. It was also able to walk through safe zones but it put its weapon away when it was walking. I don't think its an event, I think it'll be a config somewhere that isn't adjusted correctly. Next I encounter the issue I'll do some experimenting.
From what I can see the mob spawn for it is under the Golden monsters. Look for Death King in the monstersetbase.txt and if it has the map ID of 0, remove the list entry or change coordinates.
For example, this is the one I found:
The reason it is spawning is because the PvP area has the same attribute as the open area where monsters attack, so the game knows it can spawn there.Code:55 0 30 132 83 132 83 -1 1 // Death King => Lorencia 56 0 30 132 83 138 90 -1 5 // Death Bone => Lorencia
So for your problem, you want to try and find the monsters that are appearing there for you, and check if the map ID is 0, then delete the spawn or edit coordinates.
Was the gameserver offline when you did this? Try a fresh start. Otherwise I am out of ideas at the moment, sorry, :(.
Sorry man, I have no idea what else it might be.