title: Is it possible to use the same form in two different windows in Extjs4?
body: <p>I have a table with a button to add a new element and another in the row to edit the element. Those actions shares the same form with the only difference that in edit mode the form is filled. When the user clicks on the button a new window is shown with the form.</p>
  
  <p>The first time that i click the button, for example, to add a new element, works fine. The form is shown. But... if i close the window and i try to edit a user, appears an extrange window without content and an error <strong>"TypeError: b is null"</strong> Is it a problem with the definition of the form? Maybe the form istance is deleted with the window?</p>
  
  <p>I've a form defined in a var:</p>
  
  <pre><code>var formPanel =  Ext.create('Ext.form.Panel',{
       extend: 'Ext.form.Panel',
       id: 'policyForm',
       ...
  </code></pre>
  
  <p>I have a button in the tbar of the grid to show the window in order to add an user and another button in the row to edit him. This is the handler of the button:</p>
  
  <pre><code>handler : function(){
      Ext.create('Ext.window.Window',{
          layout: 'fit',
          title: 'New Policy',
          items: [formPanel],
          width: 650,
          height: 500,
          id: 'myPolicyWindow'
      }).show();
  }
  </code></pre>