There's a stange behavior with the landing page. It does not seem to take as landing page the first of the navigation ordering list.
First I had a group without an avatar, I enabled extras in this group, confirgured the extras and then added an avatar. Not sure if it ws related, but after the avatar was uploaded, the link from the group lists and directory lead to an error page though displaying the group's navigation menu.
Then I recreated a group, added an avatar and then enabled extras. Added custom pages did not change the first item on the navigation list. The home page (landing page from group directory) pointed to the group's custom pages.