Though context xml is removed and then added with new headers, the headers are not acknowledged.

Works fine for the other default context json and all new context switches though:

 
$contextSwitch->removeContext('xml');
$contextSwitch->removeContext('json');

        $context = 'xml';
        $spec = array(
            'headers'       => array(
                'Content-type' => 'text/xml',
                'Expires' => 'Mon, 26 Jul 1997 05:00:00 GMT',
                'Last-Modified' => gmdate( 'D, d M Y H:i:s' ) . ' GMT',
                'Cache-Control' => 'no-cache, must-revalidate',              
                'Pragma' => 'no-cache'   
            ),
            'callbacks'     => array(
                'post'          => array($this,'showXml')
            )
        );
        $contextSwitch->addContext($context, $spec);

        $context = 'json';
        $spec = array(
            'headers'       => array(
                'Content-type' => 'text/json',
                'Expires' => 'Mon, 26 Jul 1997 05:00:00 GMT',
                'Last-Modified' => gmdate( 'D, d M Y H:i:s' ) . ' GMT',
                'Cache-Control' => 'no-cache, must-revalidate',              
                'Pragma' => 'no-cache'                 
            ),
            'callbacks'     => array(
                'post'          => array($this,'showJson')
            )
        );
        
        $contextSwitch->addContext($context, $spec);

wrong for xml:
curl -I "http://url/format/xml"
HTTP/1.1 200 OK
Date: Mon, 03 Aug 2009 09:17:30 GMT
Server: Apache
Vary: Accept-Encoding
Content-Type: text/xml

correct for json:
curl -I "http://url/format/json"
HTTP/1.1 200 OK
Date: Mon, 03 Aug 2009 09:17:28 GMT
Server: Apache
Expires: Mon, 26 Jul 1997 05:00:00 GMT
Last-Modified: Mon, 03 Aug 2009 09:17:28 GMT
Cache-Control: no-cache, must-revalidate
Pragma: no-cache
Vary: Accept-Encoding
Content-Type: text/json