[jQuery] Trouble with draggable containment

I have a test page that demonstrates the problem: http://www.hindbrain.net/ex10.php

I have containment: 'parent' for the draggable div. If you try to move
it, it jump above
the body (window), out of sight. I've had different sizes for parts of
this page and often
you can see it poking down from the top of the screen. How can I get
this containment to
work?

thanks,
Bob