That's actually a Chuck question. It's legit and necessary if not
exactly the original meaning of the flag. Changing the vertical
shadow width is going to shift the starting pixel position of the
non-divider area of any window the change is made to. This is
effectively the same as just changing the horizontal column width of a
vertically split window. Since that action is going to cause the
windows_struture_changed flag to get set so too should changing the
vertical divider pixel width.
-Chuck