I don't think this is a case of QF's systems not being up to scratch.
I think this is a case of a conscious decision by QF throughout their booking process to make the booking class opaque. The marketing spin would be to make it "simpler" - they have been pushing the idea of fare "categories" ie Flex, Saver, Business Flex, etc and going away from specifics - which on the surface seems like a good idea, because Joe Public doesn't care if his Flex Y ticket is in Y, B, H, M etc just that it's Flex.
However this idea falls apart totally when it comes to the FF side of things who make it clear not all categories are not the same, and not on all partners, and so on. and then break it doen to the fare classes, as they always have done. Then you're scrambling to know well was it a K fare or an M fare?
My gut feel is that the whole design of the process including the ticket receipt has been driven by marketing.
We all know how easy and useful it would be to both show the booking class prior to booking, and on the receipt (and heck it still shows up in MMB, but you have to know to look for it) but no they won't.
It's very frustrating, but I think this is not a technical issue, but a design choice. Either benign ("Lets make it easier and less complex") or less so ("Let's HIDE the booking class on purpose...")