undefined behaviour in GtkFileSelection?

[Marcus vA <mva121 gmx net>]

Hello,

I'm receiving an undefined behaviour in a GtkFileSelection using 
gtk 2.2.1. Sometimes it works, most times I'm getting segfaults like
this:
---
Program received signal SIGSEGV, Segmentation fault.
0x2820d7f1 in gtk_tree_view_get_type ()
from /usr/X11R6/lib/libgtk-x11-2.0.so.200
---
Program received signal SIGSEGV, Segmentation fault.
0x2851d4ea in pango_item_free () from
/usr/X11R6/lib/libpango-1.0.so.200
---
Program received signal SIGSEGV, Segmentation fault.
0x28226ac3 in gtk_widget_unrealize () from
/usr/X11R6/lib/libgtk-x11-2.0.so.200

The necessary code:

void
_lpref_add_lesson_file (GtkWidget* widget, gpointer data)
{
  /* opens the default gtk-2 file selection dialogue */
  GtkWidget* file_select;

  file_select =  gtk_file_selection_new ("Add Lesson file");
  
  g_signal_connect (G_OBJECT (GTK_FILE_SELECTION
                    (file_select)->ok_button), "clicked",
                    G_CALLBACK(_lpref_add_lesson), file_select);  
  
  g_signal_connect_swapped 
    (G_OBJECT (GTK_FILE_SELECTION (file_select)->ok_button),
     "clicked", G_CALLBACK (gtk_widget_destroy), file_select);  
  
  g_signal_connect_swapped 
    (G_OBJECT (GTK_FILE_SELECTION (file_select)->cancel_button),
     "clicked", G_CALLBACK (gtk_widget_destroy), file_select);

  gtk_widget_show (file_select);
  return;
}

void
_lpref_add_lesson (GtkWidget *widget, GtkFileSelection* select)
{
  /* call the internal function with the selected file */
  data_add_lesson_file 
    ((char *) gtk_file_selection_get_filename 
                (GTK_FILE_SELECTION (select)));

  return;
}

Using a gtk_widget_destroy (GTK_WIDGET (select)); in _lpref_add_lesson
and removing the g_signal_connect_swapped from the ok_button results in
the same behaviour.

Any idea, where I'm worng with my code?

Regards
Marcus

---
Mr. Cole's Axiom:
The sum of the intelligence on the planet is a constant; the
population is growing.

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