GDK_Up/Down works only with GDK_CONTROL_MASK. Why?

[<back zeus nuclear kth se>]

Hi,

I have a problem with setting up a key accelerator for a menu_item.
I can use the combination of CTRL-button/Up-arrow-key without 
problem if I use:

gtk_widget_add_accelerator (GTK_WIDGET (display_menu_item_zoom_y), "activate", accel_group,GDK_Up, GDK_CONTROL_MASK, GTK_ACCEL_VISIBLE);


But if I try to use the Up-arrow-button without CTRL-button like this:

gtk_widget_add_accelerator (GTK_WIDGET (display_menu_item_zoom_y), "activate", accel_group,GDK_Up, 0, GTK_ACCEL_VISIBLE);

it does not work. Nothing happens when I press the Up key.

Why is this?

Is '0' not the correct way of saying 'no modifier key'?

The behaviour is exactly the same for GDK_Up, GDK_Down, GDK_Right, and GDK_Left.
Other keys (GDK_Z, GDK_X, etc) on the other hand, seem to work fine, both 
with CTRL and without.

(I should perhaps say that I had to include the key syms 'manually' with
#include <gdk/gdkkeysyms.h>
to get key syms to work at all. I don't know if this is related to
the problem.)

I'm running fluxbox on Debian (Woody) Linux with GTK+ 2.0.

Can Anyone help?

Regards,

Torbjoern