Can't get splitting to work with nnmaildir

[Yury Bulka <setthemfree@privacyrequired.com>]

Dear list,

I fetch my mail locally with an external program (mpop) that puts it
into ~/.Mail/INBOX which is symlinked to ~/.nnmaildir/primary. This
works fine.

Now I'm trying to make Gnus put mail from a certain mailing list
to a separate group ("list.sc").

With this config:

    (setq gnus-select-method 
          '(nnmaildir "primary"
                       (directory "~/.nnmaildir/")
                       (get-new-mail t)))
    (setq mail-sources '((file)))
    (setq nnmail-split-methods
          '(("list.sc" "^List-Id:.*sc-users\.create\.ucsb\.edu.*")
            ("primary" "")))

When I run `gnus-summary-respool-trace` on a message from that list, it
correctly reports "This message would go to list.sc".

However, when I hit B r (gnus-summary-respool-article) the message just
gets put back into "primary" instead of "list.sc" group.

Will be very grateful for any suggestions on what I'm doing wrong here.

Thanks,
Yury.

P.S. Someone has asked a similar question before, but it got lost:
http://thread.gmane.org/gmane.emacs.gnus.general/68878