- due to the aggressive object deallocation the request object and its curl handle

- due to the aggressive object deallocation the request object and its curl handle
  would already have been cleaned up when reaching curl_multi_remove_handle()
  when there's no additional reference to the request object (i.e. no user space
  reference to the attached request object);
  e.g.: $pool = new HttpRequestPool(new HttpRequest('...'))