Popup resizes to improper height on window size change

import QtQuick 2.6
import Qt.labs.controls 1.0

ApplicationWindow {
    id: main

    visible: true
    width: 640
    height: 480

    Popup {
        id: popup

        property bool isLandscape: ApplicationWindow.window.width > ApplicationWindow.window.height
        x: (ApplicationWindow.window.width - width) / 2
        y: (ApplicationWindow.window.height - height) / 2
        padding: 0
        margins: 0
        closePolicy: Popup.NoAutoClose
        contentItem: Rectangle {
            implicitWidth: popup.isLandscape ? 400 : 200
            implicitHeight: popup.isLandscape ? 200 : 400
            color: "red"
            border {
                width: 1
                color: "green"
            }
        }
        Component.onCompleted: open()
        onWidthChanged: console.log("width", width)
        onHeightChanged: console.log("height", height)
    }
}