get a blank window after recall set_visible(true)

[Victor Aurélio <victoraur santos gmail com>]

Why when I call window.set_visible(true); a second time is shown a blank 
window to me ?

I add some widgets to a Box and then add the box to the window:
hscales.show_all();
scale_window.add(hscales);

now in a callback I call set_visible:
scale_window.set_visible(true);

In the first time after run application the windows is shown correct, 
but after hide ( set_visible(false) ) and set_visible(true) again I get 
a blank window, why ?