I was answering your point: "The point was not so much over disclosure of the downgrade on the second sector (albeit 3 pages into the booking after display as a business fare LHR/SYD) but the reason given (no biz cabin on the MH flight) which is untrue."

"Mixed cabin itinerary" is definitely a good description of what that itinerary is, but it does not answer the concern you expressed about providing a reason for why it is offered in the first place.