title: Not able to drill down after clicking back button.
body: <p>I am not able to drill down after clicking back button. first time the drill down is working fine, but after coming back to original state drill down not working when clicking on the bar.
  <a href="http://jsfiddle.net/pravisivadasan/j8y21axp/7/" rel="nofollow noreferrer">Sample graph link is here</a></p>
  
  <pre><code>drillup: function(e) {
                  chart.xAxis[0].setCategories(protocolNames, true);
                  chart.xAxis[0].update({labels:{rotation:0}});
                  chart.yAxis[1].update({
                      labels: {
                          enabled: true
                      },
                      title: {
                          text: ''
                      }
                  });  
              }
  </code></pre>