Comment 1 for bug 820233

In a clean natty chroot:
# md5sum /etc/update-motd.d/00-header
4241925109d5d9fc869f20143dbd4054 /etc/update-motd.d/00-header
# md5sum /etc/update-motd.d/10-help-text
918a1e4bc361b759adff1fabbcd8fb8f /etc/update-motd.d/10-help-text
# dpkg -s base-files
Package: base-files
...
Conffiles:
 /etc/debian_version 82711d8dc3e89c428b4694a284e32541
 /etc/dpkg/origins/debian 731423fa8ba067262f8ef37882d1e742
 /etc/dpkg/origins/ubuntu ea35901c45553c3451f60476be94d2d8
 /etc/host.conf 89408008f2585c957c031716600d5a80
 /etc/issue 9865e55b7162c01dfc5ea525eb9ecee3
 /etc/issue.net 9a1459493a030337fe08477a1bc0d100
 /etc/lsb-release 7ce1ffb3689e93590b84d74fb3939302
Description: Debian base system miscellaneous files
...

So the old version did not have 00-header/10-help-text as conffiles, but the new version does:
# dpkg -s base-files (new version):
Package: base-files
Conffiles:
 /etc/debian_version 931870fda5e3f942afc004db670b3cae
 /etc/dpkg/origins/debian 731423fa8ba067262f8ef37882d1e742
 /etc/dpkg/origins/ubuntu ea35901c45553c3451f60476be94d2d8
 /etc/host.conf 89408008f2585c957c031716600d5a80
 /etc/issue 27efa0e2fe4f9b972d0b09cd75818f98
 /etc/issue.net 29f9e61bc86a4594020e6383ce9699ed
 /etc/lsb-release 362f07a83dc8ae4ae26a4b860b3ef651
 /etc/update-motd.d/00-header 4a1e6eed7a59f200b4267085721750a3
 /etc/update-motd.d/10-help-text 5064fb57493325202dded183ab0c4ebd
 /etc/update-motd.d/99-footer b0541f3c2e55c44149cd92bcc599c94c
Description: Debian base system miscellaneous files
...

But with different md5sums.