I am trying to create a Gtk::Image from a Gdk::Pixbuf and then update 
the same pixbuf. i.e.:
Gdk::Pixbuf *pixbuf;
Gtk::Image *image;
pixbuf = Gdk::Pixbuf::create_from_file("1.png");
image = manage( new Gtk::Image(pixbuf) );
pixbuf = image->get_pixbuf();

but I get:
(test:1769): GLib-GObject-CRITICAL **: file gobject.c: line 1337 
(g_object_unref): assertion `G_IS_OBJECT (object)' failed

If I create the image from a copy of the pixbuf (using pixbuf->copy in 
the image constructor), I get the same.

I submit a patch (see ChangeLog) done under guidance from Murray Cummings.
I have tested the changes with positive results.