It used to happen in Doom now and then. Now I also have the problem in Covetous lvl 3. I stealth into Covetous lvl 3, cast an Energy Vortex or two and then cast Invisibility on myself. Then I stealth outside. When I reenter the dungeon, still stealthing, one or more mobs run up to me and then they follow me everywhere I go until I make myself visible.