Gtk - Inheritance of GtkWindow

Been fiddling around with inheritance in Gtk and figured I'd make a MainWindow class. This works well except it sucks a lot of memory (around 6MB) with the code below. Just creating a new window in main() uses about 2.5MB. Any ideas why?

Also, is it a bad idea to inherit from GtkWindow and create the application around a MainWindow? Because I haven't seen many apps do it this way. Examples would be great.

Thanks

/* main.c */
 
#include <gtk/gtk.h>
 
#include "window.h"
 
gint main(gint argc, gchar *argv[])
{
	g_thread_init(NULL);
	gtk_init(&argc, &argv);
	
	GtkMainWindow* main_window;
	main_window = (GtkMainWindow*)gtk_main_window_new();
	gtk_widget_show(GTK_WIDGET(main_window));
	
	gtk_main();
	return 0;
}
 
/* window.h */
 
#ifndef WINDOW_H
#define WINDOW_H
 
#include <gtk/gtk.h>
 
#define GTK_MAIN_WINDOW_TYPE            (gtk_main_window_get_type ())
#define GTK_MAIN_WINDOW(obj)            (G_TYPE_CHECK_INSTANCE_CAST ((obj), GTK_MAIN_WINDOW_TYPE, GtkMainWindow))
#define GTK_MAIN_WINDOW_CLASS(klass)    (G_TYPE_CHECK_CLASS_CAST ((klass), GTK_MAIN_WINDOW_TYPE, GtkMainWindowClass))
#define IS_GTK_MAIN_WINDOW(obj)         (G_TYPE_CHECK_INSTANCE_TYPE ((obj), GTK_MAIN_WINDOW_TYPE))
#define IS_GTK_MAIN_WINDOW_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), GTK_MAIN_WINDOW_TYPE))
 
typedef struct _GtkMainWindow			GtkMainWindow;
typedef struct _GtkMainWindowClass		GtkMainWindowClass;
 
struct _GtkMainWindow
{
	GtkWindow parent;
};
 
struct _GtkMainWindowClass
{
	GtkWindowClass parent_class;
};
 
GtkType		gtk_main_window_get_type(void);
GtkWidget*	gtk_main_window_new(void);
 
#endif
 
/* window.c */
 
#include "window.h"
 
static void gtk_main_window_class_init (GtkMainWindowClass *klass)
{
	GObjectClass* gobject_class = G_OBJECT_CLASS(klass);
}
 
static void gtk_main_window_init(GtkMainWindow* mw)
{
	
}
 
GType gtk_main_window_get_type(void)
{
	static GType type = 0;
	if (!type)
	{
		static const GTypeInfo info =
		{
			sizeof (GtkMainWindowClass),
			NULL,
			NULL,
			(GClassInitFunc)gtk_main_window_class_init,
			NULL,
			NULL,
			sizeof (GtkMainWindow),
			0,
			(GInstanceInitFunc)gtk_main_window_init,
		};
		
		type = g_type_register_static(GTK_TYPE_WINDOW, "GtkMainWindow", &info, 0);
	}
	
	return type;
}
 
GtkWidget* gtk_main_window_new()
{
	return GTK_WIDGET(gtk_type_new(gtk_main_window_get_type()));
}

Select allOpen in new window