mode-line bug in Emacs 21

[Chong Yidong]

I recently installed Emacs 21.0.100-0.1, and have encountered a minor
bug. I realize this is not an official release; if posting an Emacs 21
bug in this newsgroup is inappropriate, I apologize.

I have the following line in my .emacs file:

(add-to-list 'default-frame-alist '(scroll-bar-width . 8))

This reduces the width of the scroll-bar. When the window is split
vertically, and the new window subsequently deleted, a portion of the
deleted mode-line remains in the space left by the shrunken
scroll-bar.

The problem does not occur if the scroll-bar is left at its default
size. However, the scroll-bar customization did not cause any problems
in Emacs 20.

Thanks,

-- Yidong