Yep. This happens quite a bit. Best advice I can give is to call reservations after leaving the RCC or ticket counter where you made the upgrade request and ask the phone agent to verify that the upgrades are properly "authorized." Happened to me and no one in Mileage Plus or reservations would help. Finally I called someone I KNEW at the RCC and he was able to fix the problem. Otherwise I would have either had to go back to the airport AGAIN or the person receiving the gift would have not been a gift receiver after all.

You're right. It's too complicated for most agents. Best bet is probably to do it in person at a 1K room, if that's possible.