PhpSpreadsheet official recipe “Write a date or time into a cell” not working as excpected

I am following the recipe Write a date or time into a cell from official PHPSpreadsheet doc.

The only difference is that the 3 writes are on 3 different cells.

PhpOfficePhpSpreadsheetCellCell::setValueBinder( new PhpOfficePhpSpreadsheetCellAdvancedValueBinder() );

$spreadsheet = new Spreadsheet();
$spreadsheet->getActiveSheet()
    ->setCellValue('D1', '2008-12-31');

$spreadsheet->getActiveSheet()->getStyle('D1')
    ->getNumberFormat()
    ->setFormatCode(PhpOfficePhpSpreadsheetStyleNumberFormat::FORMAT_DATE_YYYYMMDDSLASH);

// PHP-time (Unix time)
$time = gmmktime(0,0,0,12,31,2008); // int(1230681600)
$spreadsheet->getActiveSheet()
    ->setCellValue('D2', PhpOfficePhpSpreadsheetSharedDate::PHPToExcel($time));
$spreadsheet->getActiveSheet()->getStyle('D2')
    ->getNumberFormat()
    ->setFormatCode(PhpOfficePhpSpreadsheetStyleNumberFormat::FORMAT_DATE_YYYYMMDDSLASH);

// Excel-date/time
$spreadsheet->getActiveSheet()->setCellValue('D3', 39813);
$spreadsheet->getActiveSheet()->getStyle('D3')
    ->getNumberFormat()
    ->setFormatCode(PhpOfficePhpSpreadsheetStyleNumberFormat::FORMAT_DATE_YYYYMMDDSLASH);

$writer = new PhpOfficePhpSpreadsheetWriterOds($spreadsheet);
$writer->save("/var/www/html/var/test.ods");

Opening the ods file with LibreOffice Calc, I have the 3 cells setted with content 39813 and no date formatting is applied.

Is the doc wrong or am I missing something?