SKU sorting in admin

admin/post-types/product.php

@@ -280,7 +280,8 @@ function woocommerce_custom_product_orderby( $vars ) {
 		endif;
 		if ( 'sku' == $vars['orderby'] ) :
 			$vars = array_merge( $vars, array(
-				'orderby' 	=> 'id'
+				'meta_key' 	=> '_sku',
+				'orderby' 	=> 'meta_value'
 			) );
 		endif;
 	endif;

admin/post-types/writepanels/writepanel-product_data.php

@@ -514,7 +514,9 @@ function woocommerce_process_product_meta( $post_id, $post ) {
 	// Unique SKU 
 	$sku = get_post_meta($post_id, '_sku', true);
 	$new_sku = esc_html(stripslashes( $_POST['_sku'] ));
-	if ($new_sku!==$sku) :
+	if ($new_sku=='') :
+		update_post_meta( $post_id, '_sku', '' );
+	elseif ($new_sku!==$sku) :
 		if ($new_sku && !empty($new_sku)) :
 			if (
 				$wpdb->get_var($wpdb->prepare("

readme.txt

@@ -145,6 +145,7 @@ Yes you can! Join in on our [GitHub repository](http://github.com/woothemes/wooc
 * Bulk edit products
 * Added basic API for payment gateways to hook into (for IPN etc)
 * Added Bulgarian translation
+* Fixed SKU sort in admin
 
 = 1.4.4 - 18/02/2012 = 
 * Fix for remove coupon links after ajax update of shipping