Comment 9 for bug 468778

I dug into this a bit more tonight and here is some additional info:

If you look at the sums from releases.ubuntu.com, they're all good:

mfisch@caprica:~/Downloads/releases.ubuntu.com/oneiric$ md5sum -c MD5SUMS-metalink.releases
ubuntu-11.10-alternate-amd64.metalink: OK
ubuntu-11.10-alternate-i386.metalink: OK
ubuntu-11.10-desktop-amd64.metalink: OK
ubuntu-11.10-desktop-i386.metalink: OK
ubuntu-11.10-server-amd64.metalink: OK
ubuntu-11.10-server-i386.metalink: OK

On the other hand, all the ones from cdimage.ubuntu.com are bad:
mfisch@caprica:~/Downloads/cdimage.ubuntu.com/releases/11.10/release$ md5sum -c MD5SUMS-metalink.txt
ubuntu-11.10-alternate-amd64+mac.metalink: FAILED
ubuntu-11.10-desktop-amd64+mac.metalink: FAILED
ubuntu-11.10-dvd-amd64.metalink: FAILED
ubuntu-11.10-dvd-i386.metalink: FAILED
md5sum: WARNING: 4 computed checksums did NOT match

If you look at the datestamps for the metalink files on cdimages you will see:
13-Oct-2011 10:48
The stamp from inside the file, which metalink generates for you, matches:
Thu, 13 Oct 2011 10:48:06

But the datestamp for the MD5SUMS-metalink file is:
13-Oct-2011 10:01