title: ExtJs. JsonStore.insert() causes exception
body: <p>I have an <code>EditorGridPanel</code> with toolbar button to add new records. Everything works fine except one scenario. When I try to insert a record which already exists in database, server sends back:</p>
  
  <pre><code>{"success":false,"message":"already exists","data":{}}
  </code></pre>
  
  <p>but <code>grid</code> creates a new row marked with red triangle. If after that I try to insert a new record (even if it doesn't exist in database), everything works fine on the server side, but i get an 'uncaught exception' in firebug. It says: </p>
  
  <pre><code>'uncaught exception: Ext.data.DataReader: #realize was called with invalid remote-data. Please see the docs for DataReader#realize and review your DataReader configuration.'
  </code></pre>
  
  <p>why is that?</p>
  
  <p><strong>EDIT</strong>
  I have found that:</p>
  
  <p>When I try to insert a new record I use insert method which sends post request with parameter <code>data</code> to server (encode is true, listful is true):</p>
  
  <pre><code>data    [{"Name":"123"}]
  </code></pre>
  
  <p>and it gets from server:</p>
  
  <pre><code>{"success":true,"data":{"PositionId":"eef1d9f3-9fdf-4b87-9f6c-ef42231f4fed","Name":"123"}}
  </code></pre>
  
  <p>after that I try to create an item with the same name:</p>
  
  <pre><code>data    [{"Name":"123"}]
  </code></pre>
  
  <p>so I get:</p>
  
  <pre><code>{"success":false,"message":"already exists","data":{}}
  </code></pre>
  
  <p>from server.</p>
  
  <p>The next time I try to create the right item the store sends array with 2 items</p>
  
  <pre><code>data    [{"Name":"1234"},{"Name":"123"}]
  </code></pre>
  
  <p>but server creates only the first (newest) item and sends back:</p>
  
  <pre><code>{"success":true,"data":{"PositionId":"1ff05c7f-d5fc-41cd-81f3-faabc225b2a6","Name":"1234"}}
  </code></pre>
  
  <p>So the error may occur because store asks server to create 2 items, but only one is send back. </p>
  
  <p>So how to deal with it? is it possible to make store not to send the request for failed item again?</p>