Unable to remove all enabled GH projects

Summary of Bug

For GreenHopper classic, there is the option to select which projects are enabled/disabled. When using the option of 'Apply to these projects', the user is able to select which project can and which project cannot use the Classic Boards. However, it seems that they cannot disable all the projects

Steps to Reproduce

1. Head to the 'GreenHopper Configuration' page in your JIRA Administration
2. At the 'Enabled Projects' tab, try to first add all the projects into the 'GreenHopper Projects' list (This is because, by default, the radiobutton 'All Projects' are selected, thus no projects are in the 'GreenHopper Projects' list)
3. Then, try to remove all of them
4. When you click on 'Modify' after removing all of them, the list will turn yellow, and nothing will happen. When the screen is refreshed, the projects are back i nthe 'GreenHopper Projects' list

Additional Info

• This was tested in GreenHopper 6.2.1 and GreenHopper 6.2.2.
• I've attached a video of how the bug occurs, so that it's more convenient