When a QQuickWindowContainer is implicitly created by using child windows with the parent property, the window container won't be in the right child order relative to the parent window's child items.

import QtQuick
import QtQuick.Controls

Window {
    id: mainWindow
    width: 300; height: 300
    visible: true
    color: "darkseagreen"

    TextField {}

    Component.onCompleted: print("children ", children)

     Window {
        id: childWindow
        x: 20
        y: 30
        color: "thistle"
        parent: mainWindow
        visible: true
     }

     TextField {
        anchors.bottom: parent.bottom
     }
}
 

Expectation:

The order of the window's content item children is: TextField, WindowContainer, TextField

Actual:

The order of the window's content item children is: TextField, TextField, WindowContainer

This causes issue in the tab focus chain between the window's child items and child windows.