BuddyPress.org

Added this to the trac for you as it’s a confirmed bug. I spent a few minutes wrestling with it and found that the posting mechanism is tied to the check_is_member function, even though is_site_admin is used to make the post-form visible.

A quick fix would be to hide the post-form even for site admins, but I’d rather rebuild the access check to allow admins + group members to post on the group wire.