title: jQuery find() method not working on only one(!) class
body: <p>jQuery's find() method is not working with everything except my class <em>.szenenkasten</em>.
  It doesn't make any sense at all...</p>
  
  <p>Simplified source code:</p>
  
  <p>HTML</p>
  
  <pre><code>&lt;ul class="NavBar"&gt;
      &lt;li&gt;&lt;/li&gt;  
      &lt;li&gt;&lt;/li&gt; 
      &lt;li&gt;&lt;/li&gt; 
      &lt;li&gt;&lt;/li&gt; 
      &lt;li&gt;&lt;/li&gt;         
  &lt;/ul&gt;
  
  &lt;span class="szenenkasten"&gt;&lt;/span&gt;
  &lt;span class="szenenkasten"&gt;&lt;/span&gt;
  &lt;span class="szenenkasten"&gt;&lt;/span&gt;
  &lt;span class="szenenkasten"&gt;&lt;/span&gt;
  &lt;span class="szenenkasten"&gt;&lt;/span&gt;
  </code></pre>
  
  <p>jQuery</p>
  
  <pre><code>alert($('.NavBar').find('li').length);
   //returns 5
  alert($('.szenenkasten').find('span').length);
   //returns 0
  alert($('span').find('.szenenkasten').length);
   //returns 0
  alert($('span.szenenkasten').length);
  //returns 5
  </code></pre>