The up-to-date F.A.Q. page for PhpSpreadsheet can be found on [http://www.codeplex.com/PHPExcel/Wiki/View.aspx?title=FAQ&referringTitle=Requirements][1].
This is normal behaviour of the compatibility pack, Xlsx displays this correctly. Use \PhpOffice\PhpSpreadsheet\Writer\Xls if you really need calculated values, or force recalculation in Excel2003.