As a related rant, I flew a cheap Y sector on MH recently (KUL-BKK). I didn't expect it to credit but checked my account anyway. Nothing appeared so I filled in the claim form at ba.com to see what would happen. I received an automated response suggesting I'd already claimed for this flight, which was clearly not the case ...
So, I sent a general message via the website and received a slightly more personalised reply from someone in the UK:
Originally Posted by BA CS
"I have checked the details we have for your booking, but I'm sorry to say the fare you paid was for a booked class that does not earn Avios or Tier Points, so I am unable to credit your account.
When you fly with Malaysia Airlines only some fares will give you a booked class that earns Avios. You can see the list of classes which do earn Avios on ba.com. Your flight was booked in a deeply discounted class."
So, to cut a long story short, if you book a non-earning class it will probably just fail to appear in your account, causing you and BA unnecessary wasted time. It would make more sense to show a zero-earning entry, but hey, this is BA (or MH) IT we're talking about