Skeleton Mage corpse shooting fireballs - untargetable, never dying

There is a skeletal mage corpse in deep ravenswood lich area that died in a normal way (I killed it with a rapid fire). It then got back up and started fireballing me. It is no longer targetable with skills or auto attacks, but it regained life. It actually says "Skeletal Mage corpse" on the mob and it falls over after each attack. It can move and does follow me around the map. This is in multiplayer mode.

It appears to have stopped attacking now, but the corpse is laying on the ground with full hp showing when you click on it and has not despawned yet.

Area: Deep Ravenswood (HiddenVale_Forest02_Tier5) Loc: (-26.7, 53.3, -35.1)