in other words: - sender @ yahoo.com sends mail to mailmanlist @ somelist.com; - mailmanlist @ somelist.com appends the mailman footer to the body text/plain part; - recipient gets message, reads From addr, verifies DK sig, which now fails.
FWIW, I've seen a few mails that had multiple DK signatures, apparently as the result of going through a DK signed mailing list when the original message had also been signed.
Loren