Currently a user can only access the 'Project Members' tab of a project if that user is a project admin in the project. That creates a chicken/egg issue for new projects.

There are a few possible workarounds. In theory Horizon should show ALL projects to someone who is admin in admin when 'admin' is the current project. That may be fixable. Also, in some (future? present?) version of keystone we can add roles on the default container and just give admins 'projectadmin' on that, which would give them defacto projectadmin everywhere.