slutide

Hey guys. I was wondering if the bright minds here could give me any insight into a problem I'm having. I'm trying to book an award ticket in mid-October from STL-BHM. There is plenty of 32,500 availability on the departing leg. Coming back, Delta says there is nothing, zip, nada. Finding that odd, I check the award availability from BHM-ATL. There is plenty. I check ATL-STL. Again, wide open. What gives? Is this normal? Is Delta just blocking off awards from BHM-STL on that day? Any help anybody has would be greatly appreciated.