Author here...

Might be misunderstanding, but United is letting you change the route (X to Y) and dates between flights-- that's not the problem. What's messed up here is that United is not showing you the best prices available on the market when you're actually changing your flight, and that's regardless of what route or type of flight you're changing to.

To summarize, one of our users bought a flight and when they went to change it, United showed us the "new flight's price" as something almost twice the actual online rate if you search on United.com or GFlights.