This is expected behavior from our CDN network. You can read about the http status code 304 at: http://en.wikipedia.org/wiki/List_of_HTTP_status_codes
"304 Not Modified
Indicates that the resource has not been modified since the version specified by the request headers If-Modified-Since or If-None-Match. This means that there is no need to retransmit the resource, since the client still has a previously-downloaded copy."