Can not drag a Contacts card into a group mailing list

This a persistent problem with CONTACTS (I use Version 2539.8). Adding contact to a Group is painful or impossible. The Group list doesn't respond when a contact is dragged to the list name. Restarting Contacts works to restore once in a while. Why not add a command in the menu bar and in the right-click menu to Add Contact to List?

Whatever the fix, it should be very easy to make. Anyone out here have any other solution? Anyone at Apple paaying attention?