QWidget::isHidden() returns false when called on a top-level widget is hidden

1. Unzip, compile, and run the attached trivial-example Qt program
2. In the window that appears, click the "Show Dialog" button
3. In the QFileDialog that appears, select a file (any file) and click "Open", so that the QFileDialog becomes hidden (or alternatively click the "Hide Dialog" button in the main window; that will have the same effect)
4. Click the "Hide and then Reshow window" button in the main window
5. Click the "Show Dialog" button in the main window (a second time)
6. Observe the error dialog that appears that says "IsHiddenBugWindow::ShowDialog(): QFileDialog::isHidden() returned false when it probably should have returned true!". This indicates that the isHidden() method of the QFileDialog (which was hidden in step 3, above) has erroneously returned false. Expected behavior is for it to return true because the QFileDialog is still hidden.

Erroneous behavior is not observed in Qt 5.15.18 or 6.7.1, this is likely a regression of some kind.