05_debian_theme in unstable's grub-pc

[Brian <ad44@cityscape.co.uk>]

A portion of /etc/grub.d/05_debian_theme in grub-pc 1.98+20100804-11 has:

   # Earlier versions of grub-pc copied the default background image to /boot/grub
   # during postinst. Remove those obsolete images if they haven't been touched by
   # the user. They are still available under /usr/share/images/desktop-base/ if
   # desktop-base is installed.
   while read checksum background; do
           if [ -f "${background}" ] && [ "x`sha1sum "${background}"`" = "x${checksum}  ${
   background}" ]; then
                   echo "Removing old background image: ${background}" >&2
                   rm "${background}"
           fi
   done <<EOF
   648ee65dd0c157a69b019a5372cbcfea4fc754a5  debian-blueish-wallpaper-640x480.png
   0431e97a6c661084c59676c4baeeb8c2f602edb8  debian-blueish-wallpaper-640x480.png
   968ecf6696c5638cfe80e8e70aba239526270864  debian-blueish-wallpaper-640x480.tga
   11143e8c92a073401de0b0fd42d0c052af4ccd9b  moreblue-orbit-grub.png
   d00d5e505ab63f2d53fa880bfac447e2d3bb197c  moreblue-orbit-grub.png
   f5b12c1009ec0a3b029185f6b66cd0d7e5611019  moreblue-orbit-grub.png
   EOF

I understand what its purpose is but am unclear as to the meaning of

   . . . if they haven't been touched by the user.

as it doesn't appear possible to alter the sha1sum of a file by touching it.

The background is that I don't have the desktop-base package installed
but do have (or, rather, did have) moreblue-orbit-grub.png from the
package in /boot/grub and am inclined to think its removal is a possible
bug.