I just went through the same thing. They only charge you if you get the international leg. Of course, it's the same price whether you get the domestic leg or not ...

The bummer part was, I would assume since I had paid for an upgrade, I should have been at the top of the list for the domestic leg, and others got upgraded in front of me.

EVERY time I have tried to upgrade in the last year or so, international legs have been waitlisted until at least t-24. Inventory control is holding those seats tight in the off chance they can sell them! I am hoping now that I am Platinum, those increase a bit - it's a bit stressful to not know what cabin you will be in until boarding time!