dtstart warning on UserComments schema
===

I have the following code for rich snippet on comments:

    <ul itemscope itemtype="http://schema.org/UserComments">
        <li id="comment-1" class="comment">
            <span itemprop="name" class="author">Author 1</span>
            <p itemprop="commentText">Bla Bla Bla</p>
            <time itemprop="commentTime" content="2012-07-29" datetime="2012-07-29T05:55+00:00" title="Jul 29, 2012 5:55">2 days ago</time>
        </li>

        <li id="comment-2" class="comment">
            <span itemprop="name" class="author">Author 2</span>
            <p itemprop="commentText">yada yada yada</p>
            <time itemprop="commentTime" content="2012-07-30" datetime="2012-07-30T04:44+00:00" title="Jul 30, 2012 4:44">yesterday</time>
        </li>
     </ul>
        
According to [schema.org/UserComments][1], this is correct. However, [Google's Rich Snippets Testing Tool][2] is giving an warning:

    Warning: Missing required field "dtstart".

`dtstart` is not even a property of UserComments event. Should I ignore this warning (Google's tool is beta)? Or am I missing something?

  [1]: http://schema.org/UserComments
  [2]: http://www.google.com/webmasters/tools/richsnippets