title: Sencha touch Selectfield picker not showing correct selection
body: <p>Store of the selectfield contains <strong>same word with different case</strong> like Ed &amp; ed.When we select <strong>ed</strong>,In the picker it is showing <strong>Ed</strong>.</p>
  
  <p>Code:</p>
  
  <pre><code> Ext.create('Ext.form.Panel', {
          fullscreen: true,
          items: [
              {
                  xtype: 'fieldset',
                  title: 'Select',
  
                  items: [
                      {
                          xtype: 'selectfield',
                          label: 'Choose one',
                                      displayField:'firstName',
                  valueField:'firstName',
                          store:Ext.create("Ext.data.Store", {
                              fields: [
                  {name: 'firstName', type: 'string'},
               ],
          data : [
              {firstName: "Ed"},
               {firstName: "ed"},                   
              {firstName: "Tommy"},
              {firstName: "Aaron"},
              {firstName: "Jamie"}
          ]
      })
                      }
                  ]
              }
          ]
      }); 
  </code></pre>
  
  <p><a href="https://fiddle.sencha.com/#fiddle/kgt" rel="nofollow">Fiddle</a> for the problem</p>