WWW Windows Phone 8 / Windows RT 8.1 missing first line http status header

Not able to get the HTTP status from WWW on Windows RT 8.1 and Windows Phone 8, with unity 5.2.2f1

www.responseHeaders["STATUS"] does not exists and hidden field _responseHeaderString does not contain as first line HTTP/1.1 200 OK

responseHeaderString :

 Server: nginx
 Date: Wed, 21 Oct 2015 07:44:36 GMT
 Last-Modified: Mon, 07 Sep 2015 11:43:46 GMT
 Connection: keep-alive
 Expires: Fri, 20 Nov 2015 07:44:36 GMT
 Cache-Control: max-age=2592000
 Cache-Control: public

responseHeader :

 {
     "SERVER"       : "nginx"
     "DATE"         : "Wed, 21 Oct 2015 07:44:36 GMT"
     "LAST-MODIFIED": "Mon, 07 Sep 2015 11:43:46 GMT"
     "CONNECTION"   : "keep-alive"
     "EXPIRES"      : "Fri, 20 Nov 2015 07:44:36 GMT"
     "CACHE-CONTROL": "public"
 }

Am I missing something ?