Vector fill pattern should not be converted to bitmap when exporting from PowerPoint to PDF

When a shape is filled (e.g. tiled) with a WMF vector fill and when exporting or printing this from PowerPoint to PDF, the vector fill is converted to a bitmap at very low resolution (200 dpi).

Expected behavior: the vector fill should not be converted to a bitmap when exported to PDF, but should remain in vectorial form.

The matter has also been discussed https://answers.microsoft.com/en-us/msoffice/forum/msoffice_powerpoint-mso_win10-mso_365hp/how-to-keep-vector-fill-pattern-eg-wmfemf-when/5c8c796a-7b8f-4418-9f30-114da3da48b2?messageId=136a52e7-3b4e-46e9-8472-d39e27a2bf04&page=1&auth=1&rtAction=1618563048691.

The PowerPoint file is attached.