[AliceHoward]

I answered this on .com but some here might also like to know the answer, the problem is discussed in greater detail there but the fix is the same of course.

For this specific design layout the problem is the use of overflow hidden which can cause many problems, there is a better way of achieving the same result, the fix is as follows.

Add these following rules to additional_css template

.main2_category_content {background-image: url(themes/executivesprite/misc/bodyfill.jpg);background-position:center;background-repeat: repeat-y;margin-left: 26px;margin-right: 26px;padding: 0px;}
.clearfix:after {
   content: ".";
   visibility: hidden;
   display: block;
   height: 0;
   clear: both;
}

In areas where the pop-up is proving a problem with the frame border replace:

<div class="main_category_content">

with:

<div class="main2_category_content clearfix">