it’s odd isn’t it, but what I see - when I do flights and then add hotel is the style of check-out (with one combined price) that you get for the holiday search (maybe something to do with the fact you have connecting flights) - I don’t see what you get - with the price broken down. Who knows..
but to get the mixed cabins you either call or search mixed cabin flights and add the hotel to convert it to a holiday booking.