This is the same bug that persists everywhere.
Basically:
If there is a solid surface above where the mob is fighting, and Melee push will warp the mob immediately above you.
For example, in the hallway to 4-spawn. If you fight a giant there it will warp him on top of the lava, forcing him to run to Naggys lair, aggroing Naggy/Magi/2giants and then through the door into 4-spawn.
This can be observed in multiple places like:
Unrest - Anywhere in the house
Kael - At the Tormax or Arena archways
Even our recent Wuoshi kill:
http://www.project1999.com/forums/sh...&postcount=827
Fighting him in the ring caused him to warp on top of the dragon statue.