Custom Gallery Rendering in WP 3.5 order problem

I’m using this code to display attachments to a post in a custom gallery on a couple of sites.

<?php
$the_cat = get_the_category();
$category_name = $the_cat[0]->cat_name;
$category_description = $the_cat[0]->category_description;
$category_link = get_category_link( $the_cat[0]->cat_ID );
$url = wp_get_attachment_url( get_post_thumbnail_id($post->ID) );

	echo '<div class="titleblock-2"><p>';
	echo customTitle(50);
	echo '</p></div>';

	$attachments = get_posts(array
		(
		'post_type' => 'attachment',
		'numberposts' => -1,
		'post_status' => 'published',
		'post_parent' => $post->ID,
		'orderby' => 'post__in',
		'order' => ''
		)
	);

	if ( $attachments ) {
		echo '<div id="singlegallery">';
		foreach ( $attachments as $attachment ) {
			$attachment_page = get_attachment_link( $attachment->ID );
			echo '<div class="big-thumb"><div class="gallery-icon"><a href="';
			echo wp_get_attachment_url( $attachment->ID );
			echo '">';

			$myimage = preg_replace( '/(width|height)=\"\d*\"\s/', "", wp_get_attachment_image($attachment->ID, medium) ); echo $myimage; 

			echo '</a></div></div>';
			}
		echo '</div>';
		} 

?>

It works, but in WP 3.5 but I can’t re-order the images using the media upload tool. Changes are shown in the editor, and if I use the WP shortcode to render the gallery. Changes don’t show in my custom gallery code though and that’s the problem.

For a variety of reasons I can’t use the shortcode. All and any help appreciated.