fixed z-index positioning in newest webkit

index.html

<!-- should always be on top -->
<div class="wrapper">  
  <div class="overlay">
    overlay
  </div>
</div>

<!-- should always be in the back -->
<div class="main">
  main
</div>

style.css

.main {
  display: block;
  top: 50px;
  background-color: green;
  width: 800px;
  height: 200px;
  position: relative;
  z-index: 1;
}

.wrapper {
  position: fixed;
}

.overlay {
  left: 200px;
  background-color: blue;
  width: 200px;
  height: 500px;
  z-index: 1000;
  position: absolute;
}

demonstrating the problem with the latest changes in z-index positioning in google chrome 23:

http://updates.html5rocks.com/2012/09/Stacking-Changes-Coming-to-position-fixed-elements