Something more weird has happened to me. I bought a J flex out Y flex return last year with a stopover at DXB. Due to change in plans I had to cancel the stopover and fly to another airport(still J).

I changed the flights online and my flights were changed to F for the flight out of the UK and the next sector as well!!! ( for £20 or £30 change fee!!!!!).

At that point I assumed that since my ticket was J flex I was changed to an F saver.It could not have been an op up as it was around 40 days before the journey.

Miles were credited as Flex F!!!!!!!. I still don't know what happened . I did not pay a more than the usual fare for a J out Y return either.!!!!