I had given the dates I intended to travel and my return was about 10 days later than my arrival. When I got to LHR and put in my credit card, it spewed out the two tickets VERY quickly. Good thing I read the tickets, because the return expired three days after issuance!

I went to the ticket booth, where often you have to wait in line, and the guy stamped it as good until my return date. He said this is a problem with buying two one ways that they kept bugging the website people about and that I had needed to buy a round trip. But as I recall, the 25% discount only applied to the one way fare.

So if the HEX discount is valid, I suggest you make all round trip purchases as separate transactions and then pick up your ticket just before departure by using the specific transaction code for that direction to avoid having to wait in line at the ticket counter.

Of course, that is significantly more hassle. Poor website design, they must be taking lessons from ual.com.....