Scale widget leaves artifacts

[Juergen Salk <juergen salk gmx de>]

I have some scale widgets that leave artifacts in front
of the value display, when the slider is moved to adjust
the value. An example screenshot can be found at

  http://www.uni-ulm.de/~jsalk/temp/shot.png

(Notice the "fly droppings" in front of the 0.)

Is there a way to get rid of them? I am using gtk-1.2.10 
on Debian Woody, if that matters.

Thank you in advance.

Regards - Juergen

PS: I have appended a bare bone sample code, that I've used
for producing the screenshot above. 

#include <gtk/gtk.h>

void level_changed_cb  (GtkAdjustment *adjustment, gpointer data);

int main(int argc, char *argv[])
{
        GtkWidget *window;
        GtkWidget *hbox; 
        GtkWidget *vbox1;
        GtkAdjustment *adj1;
        GtkWidget *vscale1;

        int image_level;

        gtk_init (&argc, &argv);
        gdk_rgb_init ();

        /* build gtk gui */
        window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
        gtk_window_set_policy(GTK_WINDOW(window), TRUE, TRUE, FALSE);
        gtk_window_set_title (GTK_WINDOW (window), "Foobar");

        gtk_signal_connect (GTK_OBJECT (window), "destroy",
                        GTK_SIGNAL_FUNC (gtk_exit), NULL);

        /* main container */
        hbox = gtk_hbox_new (FALSE, 0);
        gtk_container_add (GTK_CONTAINER (window), hbox);

        /* vertical container for L scale */
        vbox1 = gtk_vbox_new (FALSE, 0);
        gtk_box_pack_start (GTK_BOX (hbox), vbox1, TRUE, TRUE, 15);

        adj1 = GTK_ADJUSTMENT (gtk_adjustment_new (image_level, 
                                        0, 50000, 1, 10, 0));
        gtk_signal_connect (GTK_OBJECT (adj1), "value_changed",
                        GTK_SIGNAL_FUNC (level_changed_cb), NULL);

        vscale1 = gtk_vscale_new (adj1);
        gtk_scale_set_digits (GTK_SCALE (vscale1), 0);
        gtk_box_pack_start (GTK_BOX (vbox1), vscale1, TRUE, TRUE, 0);

        gtk_widget_show_all (window);

        gtk_main ();

        return(0);
}

void level_changed_cb (GtkAdjustment *adjustment, gpointer data)
{
        return;
}