For some reason, local-write-file-hooks had the BBDB stuff in it, so cookies were getting added to my data…

Hmm. Test script.

(let ((old-hook local-write-file-hooks))
    (with-temp-buffer (add-hook 'local-write-file-hooks 'foo))
    (unless (equal local-write-file-hooks old-hook)
      (error "Failed test. local-write-file-hooks was modified in this buffer."))
    ;; Let's put things back the way they were
    (setq-default local-write-file-hooks old-hook))