Probably too late to help the OP, but in case it comes up in a search:
This appears to be an AA IT bug. It seems to happen when the award is held into the next day (and perhaps only if there is no longer any award seats for sale at the same rate).
If you click through the first landing screen and go to pay for the flight, it then pulls up the correct mileage amount for the reservation and not the higher amount shown on the landing screen. That's what I have found anyway. I've never had to call in when this happens.