OK, only 1 flight a day has been changed to 2 class ( up to now) and apparently it's generally the overnight flight, which explains our change as we are on the 20.25 flight. However, return flight is 7am from Dubai, so that's still a 3 class and our seat requests are not changed. Booking agent has told me that 20E/F are still good seats ( well she would!!) So, not too bothered about the change, as long as there isn't any more.