A few results have no status code defined

Ok, at least one repro case. http://book.coe.fr/conv/de/ui/frm/f5-d.htm is the URL with missing status code. Checking these URL only gives a 200 OK.

function httprl_admin_settings_form() {

  $headers = array();
  $headers['User-Agent'] = 'User-Agent: Drupal (+http://drupal.org/)';

  // Add in the headers and enable blocking mode.
  $options = array(
      'blocking' => TRUE,
      'headers' => $headers,
      'method' => 'HEAD',
      'max_redirects' => 0,
  );

  $urls = array(
    'http://www.netzgegenrechts.de',
    'http://www.nrwgegendiskriminierung.de/',
    'http://www.statewatch.org',
    'http://europa.eu.int/comm/dgs/justice_home/index_de.htm',
    'http://europa.eu.int/comm/justice_home/unit/charte/index_en.html',
    'http://book.coe.fr/conv/de/ui/frm/f5-d.htm',
    'http://www.curia.eu.int/de/',
    'http://eumc.eu.int/',
  );

  // Make sure we have enough time to validate the link.
  drupal_set_time_limit(240);

  foreach ($urls as $url) {
    // Queue up the requests.
    httprl_request($url, $options);
  }

  // Execute requests.
  $responses = httprl_send_request();
  foreach ($responses as $response) {
    krumo($response);
  }