artifacts in GNU CVS branch emacs-unicode-2

[trentbuck]

I start Emacs with a proportional font:

    emacs --enable-font-backend --font 'DejaVu Sans-8' --eval '(w3m-browse-url 
"http://en.wikipedia.org/";)'

I scroll up and down (C-v, M-v). I see 2 pixel underline to the right
of some lines.  The underlines should not be there; they are rendering
artifacts.

I press C-l, and the artifacts disappear.

I use GNU Emacs CVS branch emacs-unicode-2:

    cvs -z9 -d:pserver:address@hidden:/sources/emacs co -r emacs-unicode-2 emacs

================================================================

System Info to help track down your bug:
---------------------------------------
emacs-w3m-version
 => "1.4.149"
emacs-version
 => "GNU Emacs 23.0.0.1 (i486-pc-linux-gnu, GTK+ Version 2.10.6)\n of 
2007-01-28 on rocinante, modified by Debian"
mule-version
 => "6.0 (HANACHIRUSATO)"
system-type
 => gnu/linux
w3m-version
 => "w3m/0.5.1"
w3m-type
 => w3m-m17n
w3m-compile-options
 => ("lang=en" "m17n" "image" "color" "ansi-color" "mouse" "gpm" "menu" 
"cookie" "ssl" "ssl-verify" "external-uri-loader" "w3mmailer" "nntp" "gopher" 
"ipv6" "alarm" "mark" "migemo")
w3m-language
 => nil
w3m-command-arguments
 => nil
w3m-command-arguments-alist
 => nil
w3m-command-environment
 => nil
w3m-input-coding-system
 => utf-8
w3m-output-coding-system
 => utf-8
w3m-use-mule-ucs
 => nil