SOAPClient authentication problem

Hi,

Today I found a nasty problem with a simple php SOAP client. Never had
problems before, but today I have the following error at SOAPClient
constructor line:

SoapClient::SoapClient(http://www.w3.org/2001/xml.xsd): failed to open
stream: HTTP request failed! HTTP/1.1 401 Authorization Required

The source is as simple as:

$client = new SoapClient("http://my.host.com/my_web_service?wsdl",
                         array( 'trace' => TRUE,
                                'login'=>'mylogin',
                                'password'=>'secret'
                              )
                        );

It seems that the php xml parser tries to fetch the url
http://www.w3.org/2001/xml.xsd at wsdl parsing time. Sniffing the
network operations I found that php uses my login and password (for the
web service) also to access external references! :-O

GET /2001/xml.xsd HTTP/1.0
Authorization: Basic bXlsb2dpbjpzZWNyZXQ=
Host: www.w3.org

In the past probably w3.org just ignored the issue, but now I receive an
HTTP 401 Unauthorized error in response...

In any case it is a serious security issue if SOAPClient sends password
around the web, when the intent is that they are used only for the web
service host!

I tried the following PHP versions:

PHP 5.2.3-1ubuntu6.5 (cli) (built: Feb 11 2009 19:55:53)
Copyright (c) 1997-2007 The PHP Group
Zend Engine v2.2.0, Copyright (c) 1998-2007 Zend Technologies

PHP 5.2.8 (cli) (built: Dec 17 2008 00:54:27)
Copyright (c) 1997-2008 The PHP Group
Zend Engine v2.2.0, Copyright (c) 1998-2008 Zend Technologies
    with Zend Extension Manager v1.0.11, Copyright (c) 2003-2006, by
Zend Technologies
    with Zend Optimizer v3.2.0, Copyright (c) 1998-2006, by Zend
Technologies
    with Zend Debugger v5.2.2, Copyright (c) 1999-2006, by Zend Technologies


Regards,
Davide