This really sounds like the card you're editing isn't the one applied to the collection. Are you on a DPS contract? If so I suggest calling enterprise support and having them assist you in chasing this down.
Have you clicked the preview button in the Contents & Layouts portal after making your changes? If you don't click the preview button the changes won't come through.
The default collection never shows as a browse page. If you want a collection to show as a browse page when the app opens you have to make a collection (I usually call it "home" in the short title) and put that as the first item in the default collection. Then put your stuff in that collection.