FWIW, I've just seen this on a XEN0 box with a ex(4) ethernet adapter.
I was doing I/O test with one:
tar cf - / | rsh some_linux_box cat > /dev/null

I've done this several times today, and seen it only one. It may be related
to the packet loss rate on the link to some_linux_box.
BTW, some_linux_box is running:
Linux 2.6.10-1.9_FC2 #1 Thu Jan 13 17:54:57 EST 2005 i686 i686 i386 GNU/Linux

-- 
Manuel Bouyer <bouyer@antioche.eu.org>
     NetBSD: 26 ans d'experience feront toujours la difference
--