In drawTabNG you try to get the notebook's tab gtk_label position to correct   
it, but sometimes may be no gtk_label in the tab, getting a null pointer   
instead.  
I found it using gazpacho (http://gazpacho.sicem.biz/downloads), a gui   
designer like glade written in python. I tested it with gtk 2.4 and 2.6   
versions.  
  
To reproduce it download gazpacho, then do the following  
run gazpacho  
create a new window (toplevel widget)  
add a notebook (containers & ornaments)  
it segfaults.  
 
Backtrace: 
Reading symbols from python...done. 
Using host libthread_db library "/lib/tls/libthread_db.so.1". 
(gdb) run bin/gazpacho 
[Thread debugging using libthread_db enabled] 
[New Thread 1077078240 (LWP 19462)] 
GTK Version: (2, 6, 8) 
PyGTK Version: (2, 6, 2) 
Running Gazpacho from source tree 
Adding /usr/src/packages/BUILD/Gazpacho-0.5.3 to sys.path 
Retrieving path.py file ...  
Detaching after fork from child process 19465. 
Detaching after fork from child process 19466. 
 
Program received signal SIGSEGV, Segmentation fault. 
[Switching to Thread 1077078240 (LWP 19462)] 
0x4116e0cd in drawTabNG ()  
from /opt/gnome/lib/gtk-2.0/2.4.0/engines/libqtengine.so 
(gdb) bt 
#0  0x4116e0cd in drawTabNG ()  
from /opt/gnome/lib/gtk-2.0/2.4.0/engines/libqtengine.so 
#1  0x41169122 in draw_box ()  
from /opt/gnome/lib/gtk-2.0/2.4.0/engines/libqtengine.so 
#2  0x40820b1c in gtk_paint_box () from /opt/gnome/lib/libgtk-x11-2.0.so.0 
#3  0x41167f3f in draw_extension ()  
from /opt/gnome/lib/gtk-2.0/2.4.0/engines/libqtengine.so 
#4  0x408204e8 in gtk_paint_extension ()  
from /opt/gnome/lib/libgtk-x11-2.0.so.0 
#5  0x407e9085 in gtk_notebook_draw_tab ()  
from /opt/gnome/lib/libgtk-x11-2.0.so.0 
#6  0x407e964e in gtk_notebook_expose ()  
from /opt/gnome/lib/libgtk-x11-2.0.so.0 
#7  0x407d031e in _gtk_marshal_BOOLEAN__BOXED ()  
from /opt/gnome/lib/libgtk-x11-2.0.so.0 
#8  0x4042f457 in g_type_class_meta_marshal ()  
from /opt/gnome/lib/libgobject-2.0.so.0 
#9  0x4042fadb in g_closure_invoke () from /opt/gnome/lib/libgobject-2.0.so.0 
#10 0x40440889 in signal_emit_unlocked_R ()  
from /opt/gnome/lib/libgobject-2.0.so.0 
#11 0x4044173e in g_signal_emit_valist ()  
from /opt/gnome/lib/libgobject-2.0.so.0 
#12 0x40441d92 in g_signal_emit () from /opt/gnome/lib/libgobject-2.0.so.0 
#13 0x408b8df4 in gtk_widget_event_internal ()  
from /opt/gnome/lib/libgtk-x11-2.0.so.0 
#14 0x4073f779 in gtk_container_propagate_expose ()  
from /opt/gnome/lib/libgtk-x11-2.0.so.0 
#15 0x4073f7ad in gtk_container_expose_child ()  
from /opt/gnome/lib/libgtk-x11-2.0.so.0 
#16 0x4070015c in gtk_bin_forall () from /opt/gnome/lib/libgtk-x11-2.0.so.0 
#17 0x4074021d in gtk_container_forall ()  
from /opt/gnome/lib/libgtk-x11-2.0.so.0 
#18 0x40742275 in gtk_container_expose ()  
from /opt/gnome/lib/libgtk-x11-2.0.so.0 
#19 0x408cdc5d in gtk_window_expose () from /opt/gnome/lib/libgtk-x11-2.0.so.0 
#20 0x407d031e in _gtk_marshal_BOOLEAN__BOXED ()  
from /opt/gnome/lib/libgtk-x11-2.0.so.0 
#21 0x4042f457 in g_type_class_meta_marshal ()  
from /opt/gnome/lib/libgobject-2.0.so.0 
#22 0x4042fadb in g_closure_invoke () from /opt/gnome/lib/libgobject-2.0.so.0 
#23 0x40440889 in signal_emit_unlocked_R ()  
from /opt/gnome/lib/libgobject-2.0.so.0 
#24 0x4044173e in g_signal_emit_valist ()  
from /opt/gnome/lib/libgobject-2.0.so.0 
#25 0x40441d92 in g_signal_emit () from /opt/gnome/lib/libgobject-2.0.so.0 
#26 0x408b8df4 in gtk_widget_event_internal ()  
from /opt/gnome/lib/libgtk-x11-2.0.so.0 
#27 0x407cb303 in gtk_main_do_event () from /opt/gnome/lib/libgtk-x11-2.0.so.0 
#28 0x409ac2cd in gdk_window_process_updates_internal ()  
from /opt/gnome/lib/libgdk-x11-2.0.so.0 
#29 0x409ac43f in gdk_window_process_all_updates ()  
from /opt/gnome/lib/libgdk-x11-2.0.so.0 
#30 0x407403da in gtk_container_idle_sizer ()  
from /opt/gnome/lib/libgtk-x11-2.0.so.0