problem with admin-ajax in 3.5

Hi,

I have a problem with a function that prevents the new media library to work with 3.5 (I can’t upload nor select pictures for posts), and it seems to come from this function:

function portfolio_metabox_do_ajax_update( $form_fields, $post ) {
	?>
	<script type="text/javascript">
	    // <![CDATA[
	    jQuery.ajax({
		    url: "<?php echo admin_url( 'admin-ajax.php' );?>",
		    type: "POST",
		    data: "action=portfolio_update&id=<?php echo $post->post_parent; ?>",
		    success: function(res) {
                        jQuery('#portfolio tbody', top.document).html(res);
		    },
		    error: function(request, status, error) {
                        //console.log(arguments);
                        //alert("There was an error! Please try again.");
		    }
	   });
	   // ]]>
    </script>
	<?php
	return $form_fields;
}

Apparently (I posted this earlier, but the topic was closed before I could get a clear answer because of some morons jumping in with “hey my 3.5 doesn’t work either”), there is something happening with
<?php echo admin_url( 'admin-ajax.php' );?>
but I can’t seem to find what is wrong there.

I have 2 options: deactivate that line everywhere I don’t need it (it’s built into my theme and only need it for a certain custom post type, and will only affect the admin side), but I don’t know how. Or I can try to solve this problem. Whichever comes first… ??

Sadly, the theme developer does not answer so I’m left with trying to modify it myself…

Thank you!