opening nnimap local server initially fails

[pedro.alex.silva@gmail.com]

When I first start gnus, the connection to a local IMAP server (dovecot)
via 'shell fails. It appears that 'nnimap-stream' is set to its default
'undecided', which means it first tries to use 'ssl, leading to the
following error:

; Unable to open server nnimap+dovecot due to: dovecot/993 System error

Of course, this doesn't happen when I'm dovecot is listening on
localhost:993, but I'd rather use the tunnel method.

Here is the relevant configuration:

(setq
 gnus-secondary-select-methods '((nnimap "dovecot"
                                         (nnimap-stream shell)
                                         (nnimap-shell-program
                                          "/usr/lib/dovecot/imap")
                                         (nnir-search-engine imap))))

I then go to the server buffer and close the connection, after which
opening it again works fine, although I tipically get one or more
duplicate {nnimap:dovecot} entries.

Any ideas on what's going on? Thanks for the help.
-- 
Pedro