problem in xterm 4.2.0 pre1v4

[Giuseppe Sacco <eppesuigoccas@libero.it>]

[Please CC to me.]

Hi,
I found a problem in xterm (I think) that shows incorrectly a line as
shown in this image:
http://eppesuigoccas.homedns.org/~giuseppe/xfree420bug/xterm-4.2.0-pre1v3.png

the problem appears ramdomly but only in xterm. In the case of the Image
I just opened a new xterm and typed 
zless /usr/share/doc/xlibs/changelog.Debian.gz

I tried many times and I got the error only twice. The problem was at
differet lines (both VT100 lines and pixel lines.)

Bye,
Giuseppe

P.S. the problem was already present in pre1v3 but not in 4.1.0.1
(woody). The XFconfig driver is "sis" and the chipset SiS 630.