Yep, the bug happens to everyone. It's completly random too. Sometimes you make it to the end and fight the boss, but it all depends on where the cultist Isis spawns at.
Edit: The Amset-Ra boss has the same bug that the Kiel Hyre final boss has, if multiple people talk to the NPC that summons it, then one Amset-Ra is summoned at the end of each conversation. If 5 people talk to the NPC at or around the same time (before the first person spawns the boss and the NPC goes away), then each person that talked to the NPC will spawn the boss. So to avoid fighting 5 copies of the same thing, just have one person in the party talk to the NPC for now.
Edited by SoulHero7, 13 June 2012 - 07:25 AM.