ShapePath: Switching from a transparent colour to a non-transparent one causes the wrong colour to be displayed

import QtQuick 2.15
import QtQuick.Window 2.15
import QtQuick.Controls 2.15
import QtQuick.Shapes 1.15

Window {
    id: root
    width: 640
    height: 480
    visible: true

    property color displayColor: "yellow" // Should only show at startup

    ComboBox {
        model: ["red", "lime", "blue", "transparent"]
        onActivated: root.displayColor = currentText
    }

    Rectangle {
        anchors.centerIn: parent
        height: 100
        width: 100
        color: root.displayColor
    }

    Shape {
        anchors.fill: parent

        ShapePath {
            strokeColor: root.displayColor
            strokeWidth: 4
            startX: 0
            startY: root.height
            PathLine { x: root.width; y: 0 }

            onStrokeColorChanged: console.log("strokeColor:", strokeColor)
        }
    }
}