How to hide/unhide a widget properly

[Joao Victor <jvital gmail com>]

Take a look at these pics:
http://khiraly.4242.hu/tmp/puliAutomatic-1.png
http://khiraly.4242.hu/tmp/puliAutomatic-2.png

As you can see, the right-side widget is being hidden/unhidden, but
there's a problem: the window is growing every time the widget is
unhidden. How could i make it so that wouldn't happen? (ie., the
widgets *inside* should be resized to fit the new unhidden widget).

Cheers,
J.V.