[Reg 5.9.8 -> ] QWidget loosing contents when using winId() and re-opened

This is very similar case to QTBUG-79012 yet it seems different as the sample project in QTBUG-79012 cannot be reproduced in Qt5.15.5 while this can.

In QDialog, if you call winId() and close the dialog, the contents of the dialog are not properly displayed when re-opened.

How to reproduce
1. Use QTBUG-96286.zip
2. Click File -> Test
3. Press "winId" button -> A message dialog appears
4. Press OK to close the message dialog
5. Press "x" to close the dialog
6. Re-open the dialog from File -> Test

Actual result :
The re-opened dialog is somehow in a different size (see screenshot ) and
when expanding the dialog by dragging, it looses its contents.

Known issue

• Not reproducible on 5.9.8 just like QTBUG-79012
• This problem does not occur when using QWidget::hide()
• Workaround : Deleting and recreating the instance