I've been trying to book AA codeshares in Australia as well (SYD-CHC-SYD) using Sabre. A few minutes after I book the segments, they get automatically rejected by AA (or possibly QF). So it looks like something programmed into AA's system.
The guy at the RTW desk says that they're not going through because my previous segment is an open AA segment HNL-SYD. If that segment were to be confirmed AA (happens to be a codeshare on QF metal) then these other codeshares would go through as well.