Order variations by menu_order by fallback to ID.

includes/class-wc-ajax.php

@@ -2486,8 +2486,7 @@ class WC_AJAX {
 			'post_status'    => array( 'private', 'publish' ),
 			'posts_per_page' => $per_page,
 			'paged'          => $page,
-			'orderby'        => 'menu_order',
-			'order'          => 'ASC',
+			'orderby'        => array( 'menu_order' => 'ASC', 'ID' => 'DESC' ),
 			'post_parent'    => $product_id
 		), $product_id );
 

readme.txt

@@ -159,6 +159,9 @@ Yes you can! Join in on our [GitHub repository](http://github.com/woothemes/wooc
 
 == Changelog ==
 
+
+* Tweak - Order variations by menu_order by fallback to ID.
+
 = 2.4.3 - 12/08/2015 =
 * Fix - Query within wc_customer_bought_product().
 * Fix - Tab hiding with some theme markup.