WWW POST request headers gone on webplayer facebook

I am encountering a strange issue in my Unity game, I am trying to send some data with authorization headers to my web service in a POST request. The game is hosted in a facebook unity canvas. the request code looks like

Hashtable headers = new Hashtable();
headers.Add("Content-Type", "application/json");
headers.Add("Token", "AquiredFromFacebook");
// ... other custom headers
string data = "{#JSON encoded string#}";
WWW www = new WWW(servicelUrl, Encoding.UTF8.GetBytes(data), headers);

The problem is , in my server end , the headers are gone only if it is sent from within the facebook hosted webplayer, in the unity editor everything seemed to be OK. I am not sure what seemed to be wrong,
any help is appreciated

This is a well known bug. See Unity Issue Tracker - WWW POST request on WebPlayer built by Unity 5.0.0f2 creates an invalid request