Try to add in the head of the 404 page :
<?php header("HTTP/1.1 404 Not Found"); ?>
<base href="here-the-url-of-your-404-page"> ?
Try to add in the head of the 404 page :
<?php header("HTTP/1.1 404 Not Found"); ?>
<base href="here-the-url-of-your-404-page"> ?