title: SP2013: Default items in list are duplicated after APP update
body: <p>I'm making share-point hosted APP via MS Visual Studio.</p>
  
  <p>In app I need to have lists with default values. I'm adding them into the list by .xml under list instance.</p>
  
  <p>eg.</p>
  
  <pre><code>&lt;Data&gt;
        &lt;Rows&gt;
          &lt;Row&gt;
            &lt;Field Name="Text"&gt;Accounting&lt;/Field&gt;
          &lt;/Row&gt;
          &lt;Row&gt;
            &lt;Field Name="Text"&gt;Accounts Payable&lt;/Field&gt;
          &lt;/Row&gt;
          ....
  </code></pre>
  
  <p>After app is published to company app store catalog, installed to the team site and updated to new version, default items are duplicated.</p>
  
  <p>How can this be fixed? eg. add items only if they doesn't exists..</p>
  
  <p>Thanks!</p>