As I noted in my edited post this will occur if the OP books a return booking with US in one direction and AA in the other. As two partners are involved pricing will be based upon the multi-partner award chart. The remedy as I noted above is for the OP to not book a return (that is book the outbound as one redemption and the inbound as another redemption). Or to book a return with only one partner operating the outbound and inbound, I just did this with only US flights and the cost was 27000 avios + $33..