title: setValue points to the object instead of copying the NSString
body: <p>I'm parsing an XML document. I have an <code>NSMutableString</code> to hold the value for each node I'm passing through and for specific nodes - I want to update the <code>NewsElement</code> class.</p>
  
  <p>This is my code:</p>
  
  <pre><code>[newsElement setValue:currentElementValue forKey:elementName];
  </code></pre>
  
  <p>The currentElementValue is the <code>NSMutableString</code> the the elementName is key I want to update. Each field is <code>NSString</code>.
  The problem is that instead of copying the string, now my <code>NSString</code> points to the currentElementValue address so all of the fields are always the same...</p>