In your array, have you tried setting depth to 0 or 2?
wp_nav_menu( array( 'theme_location' => 'header-menu',
'container_class' => 'navigator',
'depth' => 2) )
Where 0 should be the default and allow unlimited submenu, and 2 would allow one submenu. I am not sure how this would happen, but if it works, perhaps somewhere the default setting for depth was set to 1.