The APP is pretty tricky on alternatives. And to make matters worse, you can 'cancel' or change your flight and the app will still show your original boarding pass. I really think United needs to do something in the APP to make it clearer when you are giving up your old seat and when you have the new one. I don't change many flights, but I go through the call center to get it done now.
The worst thing I say in the report is she spent 140,000 miles for a F seat from DC to Houston? Ouch.
A 50 min delay is pretty much ontime in UA world.