BorderImage is not updated when border values change

import Qt 4.7

Rectangle {
    width: 800; height: 600

    BorderImage {
        id: image
        border { left: 20; top: 10; right: 20; bottom: 10 }
        x: 200; y: 200
        width: 200; height: 100
        source: "button.png"

        MouseArea {
            anchors.fill: parent
            onPressed: image.border.left = 0
            onReleased: image.border.left = 20
        }
    }
}