If you read the equivalent thread on the arrse website, they seem to have no sympathy for the AAC guys on this at all. Very keen on eating their young over there! Not too surprised as aviation takes up a relatively small part of that website, they don't seem to have any grasp of the complexities of flying pay and FRI...and the concept of 'accepted in good faith'.
From what I remember when this case surfaced a few years ago, pilots applied for, and were awarded by the chain of command, flying pay which they were entitled to under the rules as they stood. Then the rules changed and a retrospective overpayment was claimed by the Treasury!