Vanishing scrollbars under Windows XT

When a scrollbar is visible but not really necessary
(whole area visible), clicking upon it destroys it under
Windows XP. The scrollbar is not redrawn later even if
scrolling becomes necessary. One is left with a hole
through which parts of the window underneath are
visible. The problem affects most of the demos supplied
with the distribution -- only a program using the dynamic
scrollbars in incrTk seems immune.