Not a bug, you have to find the right PH (difficult since they're all roaming). There's a specific spot where you park someone to watch as you kill (sorry, don't have the loc - it's between BW and SF along the wall, right next to a large boulder...which isn't really helpful, I know). The correct PH has a respawn of approx. a minute, so you need some pretty good firepower for the sake of efficiency. A full group of 54, 55+ ought to be able to do it.
The spawn cycle is the same as the one for the Enchanter epic (Felia Goldenwing), so you would wise to take some needy enchanters with you for the ride. Their spawn is a lot rarer than drops for Immortals, though, so do stick around if they're helping you. You'll basically be swimming in the stupid books by the time they get Felia. Good luck!
|