I typically fly domestically with my driver's license. My MileagePlus profile has my first and last name just like it is on my driver's license. Right now I'm on united.com trying to book an international flight and I need to use my passport which has my full middle name.

I tried to add my middle name to the flight reservation so the boarding pass matches my travel ID, but it's asking me for proof of documentation for a name change. Is this for real? I need to provide proof of a name change every time I add or delete my middle name depending on whether I'm flying domestic to match my drivers license or international to match my passport? This sounds like such a hassle unless I'm misinterpreting this. I've never run into this issue with other airlines before.