The above test site page will demonstrate the problem in IE8 only (IE 7 works fine)
If the main content area is taller than the left DIV "AND" it has form fields, the main content window will not open to the full height of the content. If you mouse around or tab around in the DIV, the main DIV will open. Also if you are in the IE Developers tools and change any attribute in the offending DIV it will open. Do not let this fool you. If I make the same change to the actual style sheet it doesn't change anything.
The DIV that is not growing is called "middle"