Comment 61 for bug 653134

The reason these extra files get placed in /boot/grub is that grub-install is called to update the wubildr file, and grub-install calls grub-install.real (for wubi) and that copies the files (in the following code grubdir is /boot/grub and pkglibdir is /usr/lib/grub/<target cpu>/):

for file in ${pkglibdir}/*.mod ${pkglibdir}/*.lst; do
    cp -f $file ${grubdir} || exit 1
done
if [ "${target_cpu}-${platform}" = "i386-pc" ] || [ "${target_cpu}-${platform}" = "sparc64-ieee1275" ] ; then
    for file in ${pkglibdir}/*.img ${pkglibdir}/efiemu??.o; do
 if test -f $file; then
     cp -f $file ${grubdir} || exit 1
 fi
    done
fi

=========================
I suppose an easy temp fix would be to change lupin's grub-install to clean up /boot/grub on the way out.