This happened to me at the Palmer House in CHI - I booked Sun-Fri at a great rate something like $169 a night on the EXE floor. I later realized that my flight Fri left at 0500 from ORD and decided to cancel 1 night at the Palmer and stay at the ORD Hilton instead. I called HHonors, no go the rate went from $169 a night to something like $350 + they said no rooms were available, same thing on the internet. I just went to the front desk when it was quiet on the 1st day of my stay and they changed it in 2 seconds.