I came across this yesterday, as I was attracted by the email offer of LON-DPS for around £1800 in business class. Having clicked through I was very annoyed to discover that this price was for mixed cabins. Calling it a business class fare when the two long sectors are in economy is very sharp practice. There may well be a demand from some for mixed cabin flights, but why not just add an extra tick box on the booking page for Mixed Cabin alongside the tick box for Premium Only? Luckily google flights seems to exclude these mixed cabin fares from business class searches.
If the QR lurker is still lurking, perhaps they can feed upwards that this gimmick is not going down well will many of the people that fly QR frequently