Windows: GDK is blocking some of WM_MOUSEMOVE

[Oved Ben Zeev <ovedbenzeev gmail com>]

Hi,
I read the following remark in gdkevents-win32.c:

    /* If we haven't moved, don't create any GDK event. Windows
       * sends WM_MOUSEMOVE messages after a new window is shows under
       * the mouse, even if the mouse hasn't moved. This disturbs gtk.
       */     
      if (msg->pt.x + _gdk_offset_x == current_root_x &&
      msg->pt.y + _gdk_offset_y == current_root_y)
    break;

Can someone explain the meaning of "This disturb gtk" - this break in the code causes the following behavior in the application:
if the mouse is over a highlighted widget and the user executes Alt+Tab that shifts to another window on top of the highlighted widget - then, when shifting back with Alt+tab
brings the application into focus without the highlight.

if this a performance hack or does it really prevents a bug in GTK behavior?

Thanks,
Oved