update data in chart (dropdown)

Question

In my code below, the data is updated but the chart is not redrawn in the same position. What is the problem in my code?

(more information in firebug if you want - json is updated when the las dropdown is changed - only the category designer have data)

 <script type="text/javascript">
    dojo.query(".estatistica").onchange(function() {
        dojo.xhrPost({
            url: "drop2.php",
            handleAs: "json",
            postData: "data=" + $(this).val(),
            preventCache: true,
            load: function(json) {
                $msgs = [];

                for (var i = 1; i < 10; i++) {
                    $msgs.push(parseFloat(json[i]["valor" + i]));
                }
                var chart1 = new dojox.charting.Chart2D('chart1');
                chart1.addPlot("default", {
                    type: "StackedAreas",
                    markers: true,
                    tension: "S",
                    lines: true,
                    areas: true,
                    labelOffset: 0,

                });
                chart1.addAxis('x');
                chart1.addAxis('y', {
                    vertical: true,
                    max: 80000
                });

                chart1.addSeries('January Visits', $msgs, {
                    stroke: 'red',
                    fill: 'pink'
                });


                chart1.updateSeries("January Visits", $msgs);
                chart1.render();


            var stackedAreaLegend = new dojox.charting.widget.SelectableLegend({
                chart: chart1
            }, "legend1");

            stackedAreaLegend.refresh();

            }
        });
    });
</script>

thanks