PropertyAnimation ignores from/to changes

import QtQuick 2.2

MouseArea {
    id: window

    width: 300
    height: 200

    Rectangle {
        id: background
        radius: 2
        clip: true
        color: "lightgray"
        width: parent.width / 3 * 2
        height: parent.height / 10
        anchors.centerIn: parent

        Rectangle {
            id: bar
            color: "lightsteelblue"
            border.color: "steelblue"
            width: parent.width / 2
            height: parent.height / 2
            anchors.verticalCenter: parent.verticalCenter

            NumberAnimation on x {
                id: anim
                from: -bar.width
                to: frame.width
                loops: Animation.Infinite
                duration: 1000
            }
        }

        Rectangle {
            id: frame
            radius: 2
            color: "transparent"
            border.color: "gray"
            border.width: 1
            anchors.fill: parent
        }
    }

    onClicked: {
        anim.stop()
        anim.start()
    }
}