title: jQuery UI z-index issue
body: <p>I am working on a tool that utilizes jQuery UI's drag/drop functionality. </p>
  
  <p>Some elements are dragged onto the main area and a new parent box is created. It is a <code>&lt;div&gt;</code> and has <code>float: left</code>. Once I create a few of such parents and continue adding children to such parent boxes, the new ones are starting to push the other boxes around. How do i prevent such behavior? </p>
  
  <p>Here's a <a href="http://www.usabilitest.com/uxvnbRC" rel="nofollow">DEMO</a>.</p>