title: Kendo stacked column chart not displaying data correctly
body: <p>Based on <a href="https://stackoverflow.com/questions/24988632/kendo-stacked-bar-chart-configuration">this</a> or similar examples I tried using kendo stacked chart.</p>
  
  <p>To my suprise the chart gets displayed incorrectly.</p>
  
  <pre><code>  $("#chart").kendoChart({
          dataSource: new kendo.data.DataSource({
              data: data,
              group: {
                  field: "Serie"
              }
          }),
          series:
          [{
              type: "column",
              stack: true,
              field: "Value"
          },
          ],
          categoryAxis: {
              field: "Category"
          }
      });
  </code></pre>
  
  <p>I tried defining also the model as in attached <a href="https://plnkr.co/edit/OmXDVwaiG1IP2nXnJN6y?p=preview" rel="nofollow noreferrer">plunker</a> or various other variations, but the data is still incorrect e.g. 2016-07 should just show 2 activities, while it shows 5.</p>
  
  <pre><code>var data =
      [{ "Category": "2016-07", "Serie": "Physiotherapy", "Value": 35.00 },
          { "Category": "2016-07", "Serie": "Flex Class", "Value": 28.00 },
          { "Category": "2016-08", "Serie": "Flex Class", "Value": 27.00 },
          { "Category": "2016-08", "Serie": "Manual Therapy", "Value": 48.00 }
  // rest in plunker
  ];
  </code></pre>