it seems that the div class="body_wrapper" resizes itself only after or while the content div's below is loaded. As this takes some time, the blue background is visible.
You can perhaps try to add a percentual height to the class...
However, my experience is that especially the IE in older versions has problems width percentual heights, so I don't know the effect this change will have.
background: none repeat scroll 0 0 #FFFFFF;
border-radius: 5px 5px 5px 5px;
height: 100%; /* added */
padding: 10px 20px;
Best Regards :-)