The chart disappears immediately after the animation

I'm trying to use chartjs, so I copied a sample code from an official document like this.

<canvas id="myChart" width="400" height="400"></canvas>
<script>
 var data = {
   labels : ["January","February","March","April","May","June","July"],
   datasets : [
 {
   fillColor : "rgba(220,220,220,0.5)",
   strokeColor : "rgba(220,220,220,1)",
   pointColor : "rgba(220,220,220,1)",
   pointStrokeColor : "#fff",
   data : [65,59,90,81,56,55,40]
 },
 {
   fillColor : "rgba(151,187,205,0.5)",
   strokeColor : "rgba(151,187,205,1)",
   pointColor : "rgba(151,187,205,1)",
   pointStrokeColor : "#fff",
   data : [28,48,40,19,96,27,100]
 }
   ]
 }
 //Get the context of the canvas element we want to select
 var ctx = document.getElementById("myChart").getContext("2d");
 var myNewChart = new Chart(ctx).PolarArea(data);
 new Chart(ctx).Line(data);
</script>

Example: http://jsfiddle.net/DerekL/FZW9z/

A chart is displayed first, but when the first animation ends, it disappears. The Javascript console shows nothing. And when the option is animationdefined false, then it appears only in seconds and disappears in the same way.

I tried on Firefox and Chrome on Mac, but the results were the same.

How does this happen, and how can I fix it?