Did you untrap the chest as well? I think there was a scroll or something in the King's drawer. That's the only thing I can think of that wouldn't be a bug / glitch. It's been so long since I played Arx, though... I don't remember if untrapping the chest would make a bit of difference unless it was a deliberately built-in mechanic to teach the player about traps and disarming them. Which I don't think it was, not that late in the intro.