Access permissions for GJ tabs

I am baffled how access is determined for the tabs on groupjive pages (Wall Events Photos Videos Files Users).
I have a dozen groupjive groups that are Open or Approval , in various categories all with identical access level, yet for almost every one of them, I am being shown a different set of tabs before I join the group. All the groups were created with all the tabs enabled.
Sometimes it shows only Members , sometimes Wall & Members, and sometimes all the tabs.

Open and Approval groups content is publicly visible. The tabs are only visible if they have content or the viewing user has permission to add content to them otherwise they'll be hidden.