When I turn mouse wheel on inverted GtkVScale/GtkHScale Widget
( applied gtk_range_set_inverted(GTK_RANGE(scale),TRUE) ),its slider moves 
opposite direction.

Test case.
/* cc scale.c -o scale `pkg-config --cflags --libs gtk+-2.0`
#include <gtk/gtk.h>

int main(int argc,char *argv[])
{
  GtkWidget *window;
  GtkWidget *vslider;
  GtkWidget *hbox;

  gtk_init(&argc,&argv);

  window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
  gtk_widget_show(window);
  hbox = gtk_hbox_new(FALSE,0);
  gtk_container_add(GTK_CONTAINER(window),hbox);
  gtk_widget_show(hbox);

  vslider = gtk_vscale_new_with_range(0.0, 100.0, 1.0);
  gtk_widget_show(vslider);
  gtk_range_set_inverted(GTK_RANGE(vslider),FALSE);
  gtk_box_pack_start(GTK_BOX(hbox),vslider,TRUE,TRUE,0);

  vslider = gtk_vscale_new_with_range(0.0, 100.0, 1.0);
  gtk_widget_show(vslider);
  gtk_range_set_inverted(GTK_RANGE(vslider),TRUE);
  gtk_box_pack_start(GTK_BOX(hbox),vslider,TRUE,TRUE,0);

  gtk_main();
  return 0;
}

I turn wheel clockwise in this program, left vertical scale's(non-inverted)
slider 
move up, but right(inverted) one move down.