Gnus-v5.9.0 fails with courier-imap-2.0.0: Error in command

[Chris Shenton <chris@shenton.org>]

I've set up courier-imap and done telnet conversations to it to verify
login.  I haven't used Gnus IMAP before but now have in gnus.el:

  (setq
   gnus-secondary-select-methods '(
                                   (nnml "") 
                                   (nnimap "pectopah.shenton.org"
                                           (nnimap-stream ssl))
                                   )
   mail-sources '((imap	:server		"pectopah.shenton.org"
                        :fetchflag	"\\Seen")
                  ...
  )


(I don't understand the difference between the secondary-select-method
and the mail-sources above, nor in the *Info* descriptions; clues?)

Anyway, Gnus prompts for password then reports an error on the
mode-line after trying to connect; it's captured in *Messages*:

  imap: Connecting to pectopah.shenton.org...
  Waiting for response from pectopah.shenton.org...done
  imap: Connecting to pectopah.shenton.org...done
  imap: Plaintext authentication...
  Imap server pectopah.shenton.org information: Fatal error: TOO MANY CONSECUTIVE PROTOCOL VIOLATIONS: 

I can watch where it fails with tcpdump; I'll just give the ASCII
here, with login omitted:

11:27:31.137415 192.168.255.185.49233 > 192.168.255.185.imap: P
1:15(14) ack 228 win 33304 <nop,nop,timestamp 5416896 5416795> (DF)

  E..B..@.@.......
  .....Q....x.Y1.u
  .....[.......R..
  .R.[1.CAPABILITY
  ..

11:27:31.138616 192.168.255.185.imap > 192.168.255.185.49233: P
228:371(143) ack 15 win 33304 <nop,nop,timestamp 5416896 5416896> (DF)

  E.....@.@..p....
  .......QY1.u..x.
  .............R..
  .R..*.CAPABILITY
  .IMAP4rev1.UIDPL
  US.CHILDREN.NAME
  SPACE.THREAD=ORD
  EREDSUBJECT.THRE
  AD=REFERENCES.SO
  RT.QUOTA.IDLE.ST
  ARTTLS..1.OK.CAP
  ABILITY.complete
  d..


11:27:31.200605 192.168.255.185.49233 > 192.168.255.185.imap: P
61:92(31) ack 602 win 33304 <nop,nop,timestamp 5416902 5416902> (DF)

  E..S..@.@.......
  .....Q....y.Y1..
  ....(........R..
  .R..4.UID.SEARCH
  .UNSEEN.UNDELETE
  D..

11:27:31.200923 192.168.255.185.imap > 192.168.255.185.49233: P
602:664(62) ack 92 win 33304 <nop,nop,timestamp 5416902 5416902> (DF)

  E..r..@.@.......
  .......QY1....y:
  .............R..
  .R..*.SEARCH.32.
  33.34.35.36.37.3
  8.39.40.41.42..4
  .OK.SEARCH.done.
  ..

11:27:31.201304 192.168.255.185.49233 > 192.168.255.185.imap: P 92:120(28) ack 664 win 33304 <nop,nop,timestamp 5416902 5416902> (DF)

  E..P..@.@.......
  .....Q....y:Y1.)
  .....p.......R..
  .R..5.UID.FETCH.
  32.RFC822.PEEK..

11:27:31.201566 192.168.255.185.imap > 192.168.255.185.49233: P 664:712(48) ack 120 win 33304 <nop,nop,timestamp 5416902 5416902> (DF)

  E..d..@.@.......
  .......QY1.)..yV
  .............R..
  .R..5.NO.Error.i
  n.IMAP.command.r
  eceived.by.serve
  r...

If I recreate this conversation over telnet, it fails likewise

  5 uid fetch 33 rfc822 peek
  5 NO Error in IMAP command received by server.

If I remove the PEEK command, it succeeds:

  6 uid fetch 33 rfc822 
  * 2 FETCH (UID 33 RFC822 {3692}
  [... shows message...]
  )
  * 2 FETCH (FLAGS (\Seen))
  6 OK FETCH completed.

I see in the CVS logs at

  http://quimby.gnus.org/cgi-bin/cvsweb.cgi/gnus/lisp/imap.el?hideattic=0

there's a mention to this in Revision 1.13:

  nnimap.el (nnimap-request-article): Use BODY.PEEK[] instead of
  RFC822.PEEK if server support IMAP4rev1.
  (nnimap-request-body): Use BODY.PEEK[TEXT] instead of
  RFC822.TEXT.PEEK if server support IMAP4rev1.
  (nnimap-request-head): Use BODY.PEEK[HEADER] instead of
  RFC822.HEADER if server support IMAP4rev1.

but it doesn't seem to be using this, despite the checks for
"IMAP4rev1" in the CAPABILITY command above.

Any suggestions or clues? Thanks.