Ignore non index.php requests

If the script executing is not index.php then do not redirect in front_page_init()

  if (!empty($_SERVER['SCRIPT_FILENAME']) && 
strpos($_SERVER['SCRIPT_FILENAME'], 'index.php', strlen($_SERVER['SCRIPT_FILENAME']) - strlen('index.php')) === FALSE) {
    return;
  }

OR

  if (!empty($_SERVER['SCRIPT_FILENAME']) && DRUPAL_ROOT . '/index.php' != $_SERVER['SCRIPT_FILENAME']) {
    return;
  }

Both work.