PHPExcel_IOFactory::createWriter causes wrong behaviour

PHP Snippet 1:

07:31:12 Create new PHPExcel object 
07:31:12 Set properties 
07:31:12 Add some data 
07:31:12 Rename sheet 
07:31:12 Write to Excel2007 format

PHP Snippet 2:

    $objWriter =  PHPExcel_IOFactory::createWriter($objPHPExcel, 'Excel2007');

    header('Content-Type: application/vnd.openxmlformats-officedocument.spreadsheetml.sheet');
    header('Content-Disposition: attachment;filename="workbook1.xlsx"');
    header('Cache-Control: max-age=0');

    ob_end_clean();
    $objWriter->save('php://output');
    exit;