Originally Posted by WannabePBA

That actually makes even less sense because with the new rules if there is an FC (not D1) seat available on a domestic flight you should have free access to that seat with a GUC.
The 5-minute question is a good one, because that would an incredibly minor change to make. I would think that wouldn't happen since there should be no logical reason why there would be no upgrade space with a 5 minute change (and that would be a punch in the face, not a slap in the face). But their revenue management can basically do whatever they want at any time I guess.

Edit: re-reading your post, I think you meant that if you want to switch your domestic flight, you'd have to re-waitlist for D1 on the international leg. Others have said that they can't re-price just one leg and they have to reprice the whole itinerary. So yes, if you are requesting a change to your domestic flight they could be saying there is no upgrade space available on the international leg now and you'll have to waitlist (same would be true with the return on the same itinerary). I also have a hard time with that because your seat that you cleared in is still your seat. Even if they have to reprice the whole itinerary they are dropping one OK/OV/OY seat and immediately giving it back to you...but that's not how they see it.