Unregistered users have rights but cannot view the Main space

Unregistered users have view rights for the whole wiki, see "wiki_rights.png". The view right is not disabled at the space level, see "main_rights.png" (the same for all other spaces). But they cannot view the Main spave, the login is required, see "login_required_for_main.png". The spaces Sandbox and Blog can be viewed, though.

Registered users only with view right are also affected.