BA is selling LHR/SYD via KUL at a slightly lower Business Class fare. This product shows as flatbeds etc for the first two pages and only on page 3 of the booking process you get to see a note that the KUL/SYD sector is in economy.
The explanation given is "This flight does not have Business. We've shown you the closest alternative." This plainly isn't true as both MH daily flights have a business cabin (wide open for bookings on most future dates) and I imagine there might be a few slightly bemused customers boarding at KUL. Why can't they be upfront about mixed cabin fares from the very first availability screen?