title: $('#id').is(':hidden') returns false even if this element is hidden
body: <p>I have the following code:</p>
  
  <pre><code>&lt;div id="foo" align="right"&gt;
      &lt;button type="button" id="bar" name="bar" title="bar" style="display:none;"&gt;bar&lt;/button&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>In IE8 <code>$('#bar').is(':hidden')</code> returns false. So I debug the jQuery source code and I found that the problem happens due to the following code:
  <code>set = ret.expr ? Sizzle.filter( ret.expr, ret.set ) : ret.set;</code>
  variable <code>set</code> is not assigned correctly.Can anyone help me? Thanks in advance.</p>