Flickable: rebound transition not always run with OS X trackpad

import QtQuick 2.6
import QtQuick.Window 2.0

Window {
    id: window
    width: 360
    height: 520
    visible: true

    ListView {
        id: listview
        anchors.fill: parent
        model: 30
        delegate: Text {
            padding: 12
            text: modelData
            font.pixelSize: 16
            width: parent.width
        }
    }

    Rectangle {
        id: scrollbar
        anchors.right: listview.right
        y: listview.visibleArea.yPosition * listview.height
        width: 10
        height: listview.visibleArea.heightRatio * listview.height
        color: "black"
    }
}