If I try to book GLA-DXB-BKK with one leg in Y and one in J, I get the following message:
Please note that your itineary (sic) has been priced on a different cabin class from the one you have requested to obtain the best fare.
and the full journey is "forced" into J.
However, if I try to book one leg in J and one in F, then no problem. Any reason for the first one not being available, and would I be able to book it by calling Emirates rather than trying to do it on-line?