Additional tab in custom module's admin configuration page
It seems that first main path 'admin/commerce/leads' needs to be defined, and then other two items added.  The first item inherits the properties of the main menu item, and the second defines its own callbacks. Far from obvious, but it works for me now:

  function leads_menu() {
  $items = array();

  $items['admin/commerce/leads'] = array(
    'title' =&gt; 'Leads',
    'access arguments' =&gt; array('administer leads'),
    'page callback' =&gt; 'leads_active',
  );
  $items['admin/commerce/leads/active'] = array(
    'title' =&gt; 'Active',
    'type' =&gt; MENU_DEFAULT_LOCAL_TASK,
    'weight' =&gt; -10,
  );
  $items['admin/commerce/leads/subscribed'] = array(
    'title' =&gt; 'Subscribed',
    'page callback' =&gt; 'leads_subscribed',
    'type' =&gt; MENU_LOCAL_TASK,
    'access arguments' =&gt; array('administer leads'),
  );

  return $items;
}