Can't use getResponseHeader()

I want to use Titanium.Network.createHTTPClient() to download a media file from a web server and save it locally. The URL's being used do not provide any clue as to what type file is being transfered. The filename and type is included in the response header. When I try to access the headers using getResponseHeader('Content-Type');, I get NULL. No matter what value I send to getResponseHeader I get NULL. I am attempting to do all this in onload. I've tried the following:

xhr.onload = function(e) {
 
Ti.API.info("Onload:"+e); //Does nothing, Ti.API.info broken.
alert(e.getResponseHeader('Content-Type'); // NULL
alert(xhr.getResponseHeader('Content-Type'); // NULL
alert(this.getResponseHeader('Content-Type'); // NULL
}