Ah, this has something to do with them not offering economy fares originating in India with validity over 3 months. I tried this about 8 months ago, DEL-DXB-DEL, and the best advice they could give me was to book J as there were no discount Y fares offered. It isn't a case of the flight being full, just EK trying to stop smart people like me booking tickets ex-India.

Though by the sound of your post, you're booking DXB-DEL-DXB, in which case this shouldn't be such a problem.