title: HIghstock flags on first point is not rendered
body: <p>I'm using HIghstock and I'm trying to put a flag in the first point defined in the series, but it is not being rendered. Elsewhere is working.</p>
  
  <p>See <a href="http://jsfiddle.net/pablorc/f9amsqms/" rel="nofollow">this jsfiddle</a> for all the info.</p>
  
  <p>In the example I coded 4 flags, one on the first and second elements and other two for the same elements but in the axis, like this:</p>
  
  <pre><code>        series: [{
              name: 'USD to EUR',
              data: data.slice(0,20),
              id: 'dataseries',
              tooltip: {
                  valueDecimals: 4
              }
          }, {
              type: 'flags',
              name: 'Flags on series',
              data: [{
                  x: Date.UTC(2003, 8, 24),
                  title: 'On first element'
              }, {
                  x: Date.UTC(2003, 8, 25),
                  title: 'On second element'
              }],
              onSeries: 'dataseries',
              shape: 'squarepin'
          }, {
              type: 'flags',
              name: 'Flags on axis',
              data: [{
                  x: Date.UTC(2003, 8, 24),
                  title: 'On first element and axis'
              }, {
                  x: Date.UTC(2003, 8, 25),
                  title: 'On second element and axis'
              }],
              shape: 'squarepin'
          }]
  </code></pre>
  
  <p>Am I doing something wrong? Is it a bug?</p>
  
  <p>Thanks in advance! :)</p>
  
  <p>EDIT:</p>
  
  <p>Same example without using Date.UTC <a href="http://jsfiddle.net/pablorc/t3j2anLk/" rel="nofollow">here</a></p>