Originally Posted by The Narwhal

Doesn't appear to be a glitch, but they've changed the flight change feature through the app. No longer can you select one flight of a multi flight itinerary to change. It now defaults to a full change and only presents the options you'd see searching the whole itinerary.

Bummer, no more changing an individual flight after the fact. That was a great feature. Guess for them it was a bug...