I still think somebody has got their wires crossed because I booked RHO-ATH-VIE this morning and when I phoned up to upgrade I was asked which flight I'd like to upgrade. As it happens I upgraded both because I have coupons to use up before I requalify for Gold, but there is nothing written in the T&Cs on the coupons themselves or anywhere else on the website.
If this new rule were true it makes no sense generally, and I think (and hope) that some agents are a little rusty with their understanding of the rules.