<p>The Unforgiven puts a curse on players that spawns ghosts. They are harmless to lvl 60 players but if a player leaves the instance and goes somewhere with low lvl players it can be used to grief them.</p>
to clarify, it's the npcs nearby unforgiven who do this curse https://database.turtle-wow.org/?spell=16336 which is not wiped upon leaving instance
Should be fixed in the next update.