xhr.getResponseHeader WWW-Authenticate not returned on the iphone

Building a digest auth application and on android, the call to xhr.getResponseHeader('WWW-Authenticate') returns the header correctly. On the iphone, the header is empty.

Seems that titanium is not returning this value for the iphone

example:

var xhr = Titanium.Network.createHTTPClient(); ... xhr.onerror = function() { if (this.status == 401) { var header = xhr.getResponseHeader('WWW-Authenticate'); } } ...