When make window fullscreen subwindow disapear some times.

[Danima]

I run this code in windows 10.
when I clicked full-screen win2 sometimes is visible some times not.
I don't want use stayTopHint flag. what should i do?

import QtQuick 2.12
import QtQuick.Window 2.15
import QtQuick.Controls 2.13

Window
{
    id:win1
    visible:true
    width:900
    height:600

    Row{
        Button
        {
            text: "Fullscreen"
            onClicked: win1.showFullScreen()
        }
        Button
        {
            text: "maximized"
            onClicked: win1.showMaximized()
        }

    }


    Window
    {
        id:win2
        visible:true
        width:200
        height:100
        transientParent: win1
        flags: Qt.Dialog 

        Rectangle
        {
            anchors.fill: parent
            color:"black"
        }

    }

}