A few years ago, I contacted CX for a quote. They insisted that I go ask QF instead as QF was the operating carrier for the first flight. They only provided the quote once I rebutted that with quotes from the fare rules and noted that the "first carrier = ticketing carrier" was only a technical limitation for the online booking tool and not any sort of "rule".

Last year, I tried to make a flight change with MH at their KLCC office - the flight to get changed being an MH flight. After the agent asked a few other people, they refused and said I had to go talk to SQ. o.O