I took me a while to see that the group panels opens always (at least here) in edit mode: edit group membership. This has been the reason for much confusion. I can remove the checkmark on that entry but I would like to open the group panel without that checkmark. I looked through configuration options but I didnot find any entry which changed this behaviour. Therefore, I ask here.
(JabRef 3.6, windows 7 6.1 amd64, Java 1.8.0_66)