I think that might just be a rumour about Man and Amsterdam but I have heard that E/F have done some M/F work, due to crew shortages on M/F.
I had heard that it was because the Haneda got reinstated earlier than BA had thought and so it left them a bit short of crew.
Who knows, BA is so keen on M/F being shown as a complete success that it is hard to find out the truth about anything!
CSMs are so keen to be better than other CSMs, that they are not telling BA about things that go wrong, so BA are really unaware of the mess that is going on on some of the flights. Having said that though many of the crew are great and all are keen, just many are very inexperienced!!