Just a random guess there with the Avios based on something I might have skimmed over in another thread / elsewhere. Not really expecting anything to be honest and might not even notice a change from say 289,416 to 289,494 Avios.

My return flight is a codeshare so that seems easier to deal with BA wise. Both flight appear in the BA app although the booking reference only shows the inbound flights on the Aer Lingus website (have to use another reference to show the outbound/inbound).

Cheap fare booked at the weekend.
BHD-LHR Aer Lingus
LHR-MEL Qantas
MEL-LHR Qantas
LHR-BHD Aer Lingus / BA

Able to select seats on the QF flights but not the codeshare flight to Belfast. Can only specify window or aisle via the Qantas website for that one.