In IE and FF I was looking at page:
http://dev.sencha.com/deploy/ext-4.0...m/dynamic.html

When I scroll to the bottom of the page I can see the Save/Cancel buttons for Form 5.
When I click on the tabs in Form 5 or Form 4 or force a validation error by typing in something other than an e-mail address in the e-mail fields it scrolls the page upwards hiding the save/cancel buttons. Scrolling down reveals them again, of course.

IE used: 7.0.5730.13CO
FF used: 3.6.13