[gtkmm] Gdk::Window::set_back_pixmap() doesn't work?

[praca_lodz op pl]

(First, I am very sorry if that issue was already subject on this list. I have tried my best to search through archives but search engine on
http://mail.gnome.org/archives/gtkmm-list/ seems not to work)

Hello,
  I'm trying to write my own SDL widget and I am aware of exposure-problem which occures (background of the widget redraws itself on SDL surface - for reference you can take a look here: http://twomix.devolution.com/pipermail/sdl/2003-December/058443.html). 
Function Gdk::Window::set_back_pixmap() should prevent widget background from redrawing itself after SDL surface but it doesn't seem to work.
quote from documentation:
"
void Gdk::Window::set_back_pixmap(const Glib::RefPtr<Pixmap>& pixmap, bool parent_relative)
(...)
May also be used to set a background of "None" on window , by setting a background pixmap of 0. 
(...) 
A background pixmap of 0 means that the window will have no background. A window with no background will never have its background filled by the windowing system, instead the window will contain whatever pixels were already in the corresponding area of the display.
"
It is not possible however to pass 0 (or NULL) to that method because it expects reference (it seems this doc is copied from gtk+ documentation verbatim). I've tried to put such a code:
gdk_window_set_back_pixmap(get_window()->gobj(), NULL, FALSE);
but it seems not to do anything.

Any help will be appriciated,
Best Regards,
  Radoslaw Grzanka