I would be really interested to know the answer to this too. I now have 2 options vouchers for the same route (DXB-India) in F class, would love to be able to go on a trip to india with a friend rather than using them constantly for cheaper flights from BOM..
I got an options voucher the other day, as I had used one of my vouchers DXB-BOM in F and once again, they changed the configuration. Basically, I got 2 free trips from the same ticket issued 2 months ago! It's worth the chance to go on the 16:10 flight DXB-BOM, apparently it happens a lot, well it must, thats the second time in a row it's happened to me!