global_timeout seems to have no effect

I see no timer_read() in the module and wonder how the module controls it's run time to make sure it exits itself clean once global timeout is reached. I also tried running link checks in linkchecker without global_timeout specified (and with background process disabled) and got a Fatal error: Maximum execution time of 240 seconds exceeded.. Something that should never happen as the default timeout is 120 seconds only.

Fatal error: Maximum execution time of 240 seconds exceeded in drupal7\sites\all\modules\httprl\httprl.module on line 1289

      $options += array(
        'global_connections' => $linkchecker_check_connections_max,
        //'global_timeout' => $max_execution_time - 30,
        'domain_connections' => linkchecker_check_domain_connections,
        'callback' => array(
          array(
            'function' => '_linkchecker_status_handling',
          ),
          $link, // This need to be passed or it's not send back to _linkchecker_status_handling()
        )
      );

It looks like the global_timeout has no effect and this also explains why the named lock do not get removed and the watchdog messages are not written.