Custom properties are missing in xls but do exist in xlsx

[codexp]

This is:

- [x] a bug report
- [ ] a feature request
- [x] **not** a usage question (ask them on https://stackoverflow.com/questions/tagged/phpspreadsheet or https://gitter.im/PHPOffice/PhpSpreadsheet)

What is the expected behavior?

After setting custom properties, I find them in file's custom properties.

What is the current behavior?

This works for xlsx format, but doesn't for xls.

What are the steps to reproduce?

• set custom properties
• save as xls
• open file in office
• open custom properties dialog

Please provide a Minimal, Complete, and Verifiable example of code that exhibits the issue without relying on an external Excel file or a web server:

<?php

require __DIR__ . '/vendor/autoload.php';

// Create new Spreadsheet object
$spreadsheet = new \PhpOffice\PhpSpreadsheet\Spreadsheet();

$spreadsheet->getProperties()
    ->setCustomProperty('Exported', time(), \PhpOffice\PhpSpreadsheet\Document\Properties::PROPERTY_TYPE_DATE)
    ->setCustomProperty('Version', '1.0')
;

$writer = new \PhpOffice\PhpSpreadsheet\Writer\Xls($spreadsheet);
$writer->save('spreadsheet.xls');

Which versions of PhpSpreadsheet and PHP are affected?

1.8.2

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.
If this is still an issue for you, please try to help by debugging it further and sharing your results.
Thank you for your contributions.

[IvanRibkov]

This bug is still present in PHP 7.4.33 + PhpSpreadsheet 1.28. Custom properties work fine for xlsx and ods formats but don't work for xls format. Tested on LibreOffice 6.4.7.2 and Microsoft Office 2003.