Custom Perspective lacks scrollbar

We created a custom perspective in the cms, as the dev-manual says. So far so good. Is the content higher than the browser-window, no scrollbar appears (as it does on all other (non custom) perspectives.
I can see, that our perspective misses several div-tags with css-classes starting all with yui-layout-*, whicht tells me, there is one or another process not starting, or the demo misses some html-code?!
Can anybody help?

Kind regards, Tanja