title: highcharts tooltip not working after zoom
body: <p>I have a problem with the highcharts column range tooltip after zoom in. 
  Basically after I zoom in (zoomType:'xy') on the column range chart, for some columns the tooltip shows up, while some others the tooltip just simply refuse to popup. I tried debug into it and the tooltip.positioner function didn't get called.</p>
  
  <p>To <a href="http://jsfiddle.net/gh/get/jquery/1.7.2/highslide-software/highcharts.com/tree/master/samples/highcharts/demo/columnrange/" rel="nofollow">try it</a>.</p>
  
  <p>copy the following and run it.</p>
  
  <pre><code>$(function () {
      window.chart = new Highcharts.Chart({
          chart: {
              renderTo: 'container',
              type: 'columnrange',
              inverted: true,
              zoomType: 'xy'
          },
  
          xAxis: {
              categories: ['Jan', 'Feb', 'Mar']
          },
  
          legend: {
              enabled: false
          },
  
          series: [{
              name: 'Temperatures',
              data: [
                  [-9.7, 9.4],
                  [-8.7, 6.5],
                  [-3.5, 9.4]
              ]
          }]
      });
  });
  </code></pre>
  
  <p>Now try to zoom and you'll notice sometimes the tooltip on some specific column wouldn't show up.</p>
  
  <p>Any advice?</p>