'What's this' help breaks QtQuick.Window (type:Qt.dialog)

A QtQuick.Window with type Qt.dialog will show a '?' button on Windows.
Clicking on it will change the mouse cursor. However, since handling of 'What's This' is not implemented, the mouse cursor will never change back.

Problem analysis:

• '?' button because, in the Windows platform plugin, Qt::WindowContextHelpButtonHint is set for top-level windows with flag Qt::Dialog.
• If the user clicks the '?' button a EnterWhatsThisMode is created (see QWindowSystemInterface::handleEnterWhatsThisEvent)
• QApplication::event handles QEvent::EnterWhatsThisMode by calling QWhatsThis::enterWhatsThisMode();
• QWhatsThis only forwards events to top level QWidgets (QApplication::topLevelWidgets()). So even if QWindow / QQuickWindow would add event handlers for QEvent::QueryWhatsThis, QEvent:WhatsThis it would not be delivered

Workaround:

Explicitly disable Qt::WindowContextHelpButtonHint for QtQuick.Window objects

Window {
    flags: Qt.Dialog

    Component.onCompleted: {
        flags = flags & ~Qt.WindowContextHelpButtonHint
    }
    // ...
}