My experience a couple of years ago on an MH codeshare from KUL to MEL on a TK ticket was that there was no way to do seat selection - getting a boarding pass at the transit desk in KUL was the only way - and of course, this meant I was down the back of the bus.

Even worse, no points accrued to a non-TK FFP due to *A relying on operating carrier (MH) while OW relied on marketing carrier (TK). A total ****show.