I have the exact same problem. On a page that has a RadTab strip and I am using the RadWindow as container, just like in your samples. There is a RestrictionZoneID set and all is well on the first tab click.
Each time a click is done on any tab, the RadWindows move up and up with each click. IT eventually becomes unusable as the window covers all the tabs.
I am following your demo exactly and copied the code as it is from this demo.
I am using the latest update as of 3/18 2009 for the controls.