From "My Apps", I click on "Manage my billing account" > Manage Billing Account Summary tab > Groups > "The name of the group" > List Applications Accessible to this Group > Select 'Search for text in the name or description of an application' and I search for "The name of my app" > Search > Select 'Add' in Search Results > taken back to "My Apps" page.
It's like a circle. Everything in the instructions about adding an app to a group is correct right up to select 'Add' in Search Results, which takes me back to "My Apps" page and the app is not added to my group.

