Moderated Group 404 errors

Hi all- the Google Summer of Code mentors group (http://groups.drupal.org/soc-2009-mentors) is set to "moderated" for the group type, however, when people who aren't members visit the page they don't receive an option of joining (instead they get a 404 access denied error). Am I missing something? Is it not possible to have a g.d.o group both open to applications to join and keep it private? If not I'll simply put up a post on the soc group and ask people to e-mail me to join.