Display popup message shows wrong content.

Because the line_items were concatenated,
the last added item doesn't have to be the item the message was shown.

So I chose to take the last changed item instead. Because I did not use git on the machine, here is the src code from line 880 following in dc_ajax_add_cart.module:

/**
 * Returns the last line item that was changed to cart.
 *
 * @param object $line_items_wrapper
 *   Entity list wrapper of line items.
 *
 * @return object
 *   The last line item.
 */
function dc_ajax_add_cart_get_last_line_item_wrapper($line_items_wrapper) {
  $result = $line_items_wrapper->value();
  $changed = 0;
  foreach ($result as $key => $value) {
    if($value->changed > $changed){
      $last_changed_key = $key;
      $changed = $value->changed;
    }
  }
  return $result[$last_changed_key];
}