$_SERVER['QUERY_STRING'] 

Does not contain XHTML 1.1 compliant ampersands i.e. &

So you will need to do something like this if you are to use $_SERVER['QUERY_STRING'] in URL's.

//  XHTML 1.1 compliant ampersands 
$_SERVER['QUERY_STRING'] = 
str_replace(array('&', '&'), array('&', '&'), 
$_SERVER['QUERY_STRING']);