GtkTreeStore/GtkTreeModel problem in C

[Tvrtko MajstoroviÄ <t m nixstuff gmail com>]

I'm having a problem with my application that uses GtkTreeView which is 
connected to one GtkTreeStore. I created GtkTreeStore as a global 
variable so I can access to it from all parts of my project. Is that 
right? or wrong? I'm new to GTK+. Basically I understand most of the 
widgets I encountered but this one (tree views and tree models) are 
giving me a headache.
I'm using Anjuta with libglade. I created gladefile with treeview in it, 
and created "init_tree" function that initializes "treeview1" and as 
said before one global "GtkTreeStore * media_catalog":

GtkTreeStore * media_catalog;

void
init_tree ( GtkWidget * view)
{
   GtkTreeViewColumn *col;
   GtkCellRenderer *renderer;

   col = gtk_tree_view_column_new();
   gtk_tree_view_column_set_title(col, "Stored Media");
   gtk_tree_view_append_column(GTK_TREE_VIEW(view), col);

   renderer = gtk_cell_renderer_text_new();
   gtk_tree_view_column_pack_start(col, renderer, TRUE);
   gtk_tree_view_column_add_attribute(col, renderer,
                                         "text", 0);

   media_catalog = gtk_tree_store_new ( 1, G_TYPE_STRING);
   gtk_tree_view_set_model( GTK_TREE_VIEW ( view),
                            GTK_TREE_MODEL ( media_catalog));
  
   g_object_unref ( media_catalog);
}

now... I have this:

GtkWidget*
create_window (void)
{
   GtkWidget * window;
   GtkWidget * view;
   GladeXML * gxml;
  
   gxml = glade_xml_new ( GLADE_FILE, NULL, NULL);
  
   /* This is important */
   window = glade_xml_get_widget ( gxml, "mc-window");
   view = glade_xml_get_widget ( gxml, "treeview1");
   init_tree ( view);
   glade_xml_signal_autoconnect ( gxml);
  
   return window;
}

so when I call:

GtkWidget *window = create_window();
// ... connect delete and destroy events ...
gtk_widget_show (window);

... the tree view "treeview1" is displayed as predicted.

Next, the app uses one more dialog window that needs to add more info to 
the "media-catalog" store. In that dialog I have a button, with signal 
handler like this:

void
on_add_button_clicked (GtkWidget * widget,
                      gpointer data)
{
   GtkTreeIter iter;
  
   gtk_tree_store_append ( media_catalog, &iter, NULL);
   gtk_tree_store_set ( media_catalog, &iter, 0, "hahaha", -1);
}

but, when clicked nothing shows up in the "treeview1". Can anyone help 
me, direct me in right direction? please!