I believe the OP is talking about an AAdvantage one world award (quite why this is in OW forum and not in AAdvantage forum I don't know), not a paid fare.

Who knows how the computer is programmed for complex itins like this. If you are going to create complex routings to maximise your value you have to expect sometimes to run up against limits of computer. No problem with paper ticket, but the OP wanted an e-ticket.