I couldnt get the DXB-AKL flight, so return is routing via MEL (AKL-DXB -> DXB-MEL -> MEL-AKL)

MEL-AKL is a QF flight, with EK code share

I can see all the flights on both qantas.com/emirates.com, and choose seats (but can only change the MEL-AKL flight on the QF site)