<!-- Changes in Product Controller -->
  <file path="admin/controller/catalog/product.php">
    <operation>
      <search index="0,10"><![CDATA[if (isset($this->request->get['filter_model'])) {]]></search>
      <add position="replace"><![CDATA[
      /* Filter by Categories and Manufacturers */
      if (isset($this->request->get['filter_category'])) {
        $filter_category = $this->request->get['filter_category'];
      } else {
        $filter_category = null;
      }

      if (isset($this->request->get['filter_manufacturer'])) {
        $filter_manufacturer = $this->request->get['filter_manufacturer'];
      } else {
        $filter_manufacturer = null;
      }
      /* Filter by Categories and Manufacturers */

      if (isset($this->request->get['filter_model'])) {
      ]]></add>
    </operation>
  </file>