From Simon Munton as pointed out by Stephen Fisher:

patch on bug #220 (to main.c. 
the second part to packet_list.c was done separately for bug 1159 in rev 19735).  That patch fixes bug #1205 coincidentally.

svn path=/trunk/; revision=19888

gtk/main.c

@@ -3619,6 +3619,10 @@ main_widgets_show_or_hide(void)
     } else {
         gtk_widget_hide(welcome_pane);
     }
+
+    /* workaround for bug in GtkCList to ensure packet list scrollbar is updated */
+    packet_list_freeze ();
+    packet_list_thaw ();
 }