#42514 by wtanaka and dopry. More thoroughly delete custom blocks.

modules/block/block.module

@@ -541,6 +541,7 @@ function block_box_delete($bid = 0) {
  */
 function block_box_delete_submit($form_id, $form_values) {
   db_query('DELETE FROM {boxes} WHERE bid = %d', $form_values['bid']);
+  db_query("DELETE FROM {blocks} WHERE module = 'block' AND delta = %d", $form_values['bid']);
   drupal_set_message(t('The block %name has been removed.', array('%name' => $form_values['info'])));
   cache_clear_all();
   return 'admin/build/block';