Axis Flags data label issue

HTML

<script src="http://code.highcharts.com/stock/highstock.js"></script>
<div id="container" style="height: 400px"></div>

JavaScript

$(function () {
    $('#container').highcharts({
        chart: {
            type: 'line'
        },
        yAxis: {
            min: 0
        },
        xAxis: [{
            id: "1",
            categories: ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec']
        }

        ],
        plotOptions: {
            series: {
                allowPointSelect: true
            }
        },
        series: [{
            dataLabels: {
                enabled: true,
                zIndex: 2
            },
            data: [78.9, 40.5, 4.22, 129.2, 144.0, 176.0, 135.6, 148.5, 216.4, 194.1, 95.6, 87.4]
        }, {
            type: 'flags',
            showInLegend: false,
            //zIndex: 10,
            data: [{
                x: 2,
                text: 'Start of campaign'
            }, {
                x: 8,
                text: 'End of Campaing'
            }],

            width: 14,
            height: 14,
            //y: -35,
            shape: 'flag'
        }]
    });



});