title: Sencha Touch NestedList getDetailCard trouble
body: <p>I'm having a bit of trouble using a Nested List and a detailCard. I currently have a nested list displaying a simple tree of categories of CDs. It looks like this:</p>
  
  <pre><code>LCMobile.views.CategoriesList = Ext.extend(Ext.Panel, { 
      layout: 'card', 
      items: categoriesList 
  }); 
  
  var categoriesList = new Ext.NestedList({ 
      title: 'Categories',
      store: categoryStore, 
      displayField: 'title', 
      getDetailCard: function(item, parent) { 
          var itemData = item.attributes.record.data; 
          parentData = parent.attributes.record.data; 
          LCMobile.detailCard.update(itemData); 
          this.backButton.setText(parentData.title); 
          return LCMobile.detailCard; 
      } 
  });  
  </code></pre>
  
  <p>And my detailCard looks like this:</p>
  
  <pre><code>LCMobile.detailCard = new Ext.Panel({ 
      id: 'detailPanel', 
      layout: 'card', 
      scroll: 'vertical', 
      styleHtmlContent: true, 
      items: '', 
      tpl: ["&lt;h3&gt;{title}&lt;/h3&gt;", "&lt;img height='50px' width='50px' src='/images/covers/{sku}.jpg'&gt;{description}" ] 
  });  
  </code></pre>
  
  <p>Problem I am having is that the detailCard will show up once, and the back button will work, but it will only work one time, and error out after that. Says <code>
  Uncaught TypeError: Cannot read property 'style' of undefined</code>.
  I'm pretty sure there's another step I'm missing somewhere not assigning the previous card, but I'm at a bit of a loss, and in the API the only thing I could find was about the prev() method for cards, and it only made me more confused. Can anyone point me in the right direction? Thanks!</p>