Mail read by nnimap not accessible by nnfolder

[Markus Hilpert <nospam@please.not>]

Hello,

I am quite new to Gnus as a mailreader, so here is a question, I found
no answer for in the manual or the usenet.

I am reading my Emails from home via the nnimap mail backend:

(setq gnus-select-method '(nnimap "REMOTE")
      (nnimap-address "mail.myprovider.com")
      (nnimap-server-port 993)
      (nnimap-stream ssl)
      (nnimap-authenticator login)
      (nnimap-list-pattern ("INBOX"))
      )

This works, but the messages, I open, are not downloaded, when
afterwards accessing the server via the "imap"-mail source, using the
nnfolder backend, which I do at work:

(setq gnus-secondary-select-methods '((nnfolder ""))
      nnfolder-directory gnus-mail-dir-thisyear
      nnfolder-active-file (concat gnus-mail-dir-thisyear "active")
      )

(eval-after-load "mail-source"
  '(add-to-list 'mail-sources 
		'(imap
		  :server "mail.myprovider.com"
		  :port   993
		  :stream ssl
		  :user   "markus"
		  :mailbox "INBOX"
		  :dontexpunge t
		  :fetchflag "\\Seen"
		  )))

Is the message somehow flagged by nnimap, so that it won't be
downloaded afterwards via the imap-mail-source? It is still on the
server, as checked by a web-interface. Even, when via nnimap marking
the message as unread, in the "nnfolder/imap" - combination it does
not show up.

Is it possible to read my messages via nnimap, but nevertheless having
them accessible afterwards by the imap mail-source?

Thank you very much for hints!

Markus