I'm Plt, My Girlfriend is not...
The kiosk don't seem to be able to handle this, maybe not in all locations.
I have alway bought stickers to cover upgrades for both of us when I buy tickets online. Once when I did not clear, I thought maybe it was becaause my GF's account did not have enough.. So I bought her 15.
When We used the Kiosk, It said she still needed to buy 2 to cover it..
Once home, I checked. They should have come from my account to begin with..
This has happened multiple times, multiple airports (DFW,ATL,LAS,PHL,EWR,ORD,MIA,SJU)..
Funny thing about half the time after making her buy the upgrades in her account, they end up being deducted from mine anyway...
I am a software developer and write these kind of software systems for a lving, their code is jacked up..
However sometimes you find things that are broken can be used to your advantage..