Form does not render correctly in IE when attached

When rendering a form in a window object in IE, the form ends up becoming wider than the window. In Firefox, the form is correctly restricted to the width of the window object.

I have attached a demo application to illustrate the problem. Please load the demo in both browsers to see the difference.

This is with the latest 3.6 PRO build 130619.

Do you have any suggestions?
Demo.zip (214 KB)

Add correct doctype: