Hsilbiger,
Your story made me remember a similar experience (albeit at the Nusa Dua property). At the end of my stay, I got a bill with a rate substantially higher than what I had been quoted at check-in with no explanation. I wasn't able to get things resolved in the short time before I had to leave for the airport, but left feeling gipped out of an extra $1,500.
Although I am a loyal Hyatt fan in Asia, I haven't been back to the Grand Hyatt Nusa Dua, and I guess that's why.