Overriding post_gallery causes me to lose attributes

I’m overriding post_gallery in functions.php but its losing the values of the attributes. Any idea why this is happening?

function custom_gallery_shortcode_override($attr)
{
	global $post;
	$output = '';
	$lgal = '';
	$cols = 0;
	$ul_closed = false;
	$size_selected = 'tiny';

	//Extract default gallery settings
	extract(shortcode_atts(array(
		'order'      => 'ASC',
		'orderby'    => 'menu_order ID',
		'id'         => $post->ID,
		'itemtag'    => 'dl',
		'icontag'    => 'dt',
		'captiontag' => 'dd',
		'columns'    => 3,
		'size'       => $size_selected,
		'include'    => '',
		'exclude'    => ''
	), $attr));

	$attachments = get_children(array(
		'post_parent' => $id,
		'post_status' => 'inherit',
		'post_type' => 'attachment',
		'post_mime_type' => 'image',
		'order' => $order,
		'orderby' => $orderby
	));

    if (!empty($attachments))
	{
		$output .= '<div id="gal-' . $id . '" class="gal">' . "\n";
		$output .= '<ul class="gal-thumbs">';

		//Loop through each attachment
		foreach ($attachments as $image)
		{
			if ($ul_closed)
			{
				$output .= '<ul class="gal-thumbs">';
				$ul_closed = false;
			}

			$att_img = wp_get_attachment_image($image->ID, $size_selected);//img tag
			$att_url = wp_get_attachment_url($image->ID);//url to image
			$att_link = get_attachment_link($image->ID);//url to "attachment page" - page with image on it
			$postlink = get_permalink($image->post_parent);//url to post that has attachments
			$att_desc = trim(htmlentities($image->post_content, ENT_QUOTES, 'UTF-8', true));//description
			$att_cap = trim(htmlentities($image->post_excerpt, ENT_QUOTES, 'UTF-8', true));//caption
			$att_title = trim(htmlentities($image->post_title, ENT_QUOTES, 'UTF-8', true));

			$big_array = image_downsize($image->ID, 'large');
 			$large_link = $big_array[0];//large

			$output .= '<li class="gal-item">';

			echo 'link=' . $attr['link'];//DEBUG - THIS SHOWS NOTHING!!!!

			//see if gallery was set to file or not
			if (isset($attr['link']) && 'file' == $attr['link'])
			{
				//wp_get_attachment_link($id, $size, false, false);//get file
				$l = $att_url;
			}
			else
			{
				//wp_get_attachment_link($id, $size, true, false);//get permalink to attachment page
				$l = $att_link;
			}

			$output .= '<a class="gal-thumb" href="' .  $l . '" title="' . $att_title . '" data-url="' . $large_link . '">';

			$output .= $att_img;

			$output .= ' <span>';
			$output .= $att_title;

			if ($att_cap != '')
			{
				$output .= ' - ' . $att_cap;
			}

			$output .= '</span>';

			$output .= '</a>';
			$output .= '</li>' . "\n";

			if ($columns > 0 && ++$cols % $columns == 0)
			{
				$output .= '</ul>';
				$ul_closed = true;
			}
		}

		if (!$ul_closed)
		{
			$output .= '</ul>';
		}

		$output .= '</div><!--.gal-->' . "\n";
	}

	return $lgal . $output;
}

add_filter('post_gallery', 'custom_gallery_shortcode_override', 10, 2);