hmmmm, I dont know if there is anything to exploit here but.... When I was going to kill Izual there was a BlackWall outside of the Pandemonium and so I dropped a rare ring (the ring sucked) and I went to town and got healed and stuff and when the blackwall was gone the ring wasnt on the ground but where the ring was in my inventorty was mephisto's soulstone. I never had mephisto's soulstone before the blackwall and it magicly appeared in my inventory. So needless to say I lost the ring that I dropped and the game replaced the ring with mephisto's soulstone.