title: Adding menuItems to a new button affects other button
body: <p>I'm trying to add a new button (found example on <a href="http://jsfiddle.net/fXHB5/3496/" rel="nofollow">http://jsfiddle.net/fXHB5/3496/</a>)
  I want this button to have menuItems viz., 'column', 'line', 'bar', 'pie'
  When I try to add the above menuItems to new button called 'testButton' it changes the menuItems of 'exportButton' to same</p>
  
  <p>Heres my code</p>
  
  <pre><code>exporting: {
    buttons: {
    testButton: {
      menuItems: [{
        text: 'Column',
        onclick: function() {
          //ChangeChart('column');
        }
      },
      {
        text: 'Line',
        onclick: function() {
          //ChangeChart('line');
        }  
      }],
      symbol: 'diamond',
      x: -62,
      symbolFill: '#B5C9DF',
      hoverSymbolFill: '#779ABF',
      _titleKey: 'printButtonTitle'                
    },          
  
    exportButton: {
      menuItems: [,,,,{
        text: 'Download CSV',
        onclick: function() {
          //DownloadJSON2CSV(dataSeries);
        }
      }]
     } //exportButton ends here
     } //buttons ends here
    } //exporting ends here
  </code></pre>