Shelf not working properly in Snow Leopard

[Gu]

Hi all,
    I have the latest QS(B60) and make sure that I have installed the
Shelf and Clipboard. However, it doesn't work properly. When I involve
the shelf by Option+Commd+S, I can see the shelf. However, Once the
mouse pointer leave the shelf window, the shelf goes away immediately.
Did I do something wrong?
Thanks.