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;
}