1. while setting the Xserver with dual screen mode, and then launch the gnome-shell, the gnome-shell would exit.
2. this problem is identified with the following code in mutter in file display.c function meta_display_open (void)
  while (i < ScreenCount (xdisplay))
    {
      MetaScreen *screen;

      screen = meta_screen_new (the_display, i, timestamp);

      if (screen)
        screens = g_slist_prepend (screens, screen);
      ++i;
    }
3. the append operation would cause the list have a reversed sequence, which would cause the latter initialization fail.
4. although it is fix but there are more dual screen problem such as JS fail
5. it is advisable to establish a mechanism to bind the screen and the windown attributes, such as a table, etc