I agree with giving them a call and asking about it. I had a similar issue a few weeks ago. Was trying to make a reservation at POR---there were rooms available if we checked in the day before through the length of our stay, but not for the actual dates that we wanted. The next day, I tried searching rooms again and I could find availability if we came in a day later for the original timeframe we wanted, but no longer the day before. It just didn't make sense to me.
I called and talked to a cast member and they put me on hold for a while, but were able to secure the exact dates that we wanted. That was some Disney magic for us!