includes/modules/pages/checkout_success/header_php.php

suggest modifying line 99 (99-104 shown below):
Code:
  $products_query = "SELECT products_id, products_name
                     FROM " . TABLE_ORDERS_PRODUCTS . "
                     WHERE orders_id = :ordersID
                     ORDER BY products_name";
  $products_query = $db->bindVars($products_query, ':ordersID', $orders_id, 'integer');
  $products = $db->Execute($products_query);
Code:
  $products_query = "SELECT DISTINCT products_id, products_name
                     FROM " . TABLE_ORDERS_PRODUCTS . "
                     WHERE orders_id = :ordersID
                     ORDER BY products_name";
  $products_query = $db->bindVars($products_query, ':ordersID', $orders_id, 'integer');
  $products = $db->Execute($products_query);
Prevents repetitive display of the product name in an order that has the same products_id multiple times.