[Dovecot] how to store flags \Seen into read-only mailbox?

[seriv at parkheights.dyndns.org]

Hi,
I'm trying to use dovecot for storing mailing lists and read-only access for users.
The OS is Solaris, authentication for all readers of these lists are from Ldap through PAM, and one local user "listuser" will receive all mail and store them into it's folders (Maildirs). These maildirs are readable (read-only) for all others and they are shared by setting 
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mail_location: maildir:/home/vmail/listuser/Maildir:CONTROL=/home/vmail/%u/Maildir/control:INDEX=/home/vmail/%u/Maildir/index
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Mail became readable because in each mail folder to be shared there is dovecot-shared with mode 064, and all users included into his group.

But this is the problem: how to have flag \Seen stored in read-only mailbox?  As recorded by rawlog, it is ignored now:
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bash-3.00# cat 20080724-103219-10616.in
3 namespace
4 lsub "" "*"
5 list "" "INBOX"
6 list "" "Trash"
7 create "Trash"
8 select "OmniTI.FreeLotto.Ops"
9 UID fetch 1:* (FLAGS)
10 uid store 1:3 +Flags (\Seen)
11 IDLE
DONE
12 close
13 logout
bash-3.00# cat 20080724-103219-10616.out
* OK [RAWLOG TIMESTAMP] 2008-07-24 10:32:19
* NAMESPACE (("" ".")) NIL NIL
3 OK Namespace completed.
* LSUB () "." "OmniTI.FreeLotto.ODS"
* LSUB () "." "OmniTI.FreeLotto.Ops"
4 OK Lsub completed.
* LIST (\HasNoChildren) "." "INBOX"
5 OK List completed.
6 OK List completed.
7 NO Internal error occurred. Refer to server log for more information. [2008-07-24 10:32:19]
* FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
* OK [PERMANENTFLAGS ()] Read-only mailbox.
* 3 EXISTS
* 0 RECENT
* OK [UNSEEN 1] First unseen.
* OK [UIDVALIDITY 1216906857] UIDs valid
* OK [UIDNEXT 4] Predicted next UID
8 OK [READ-ONLY] Select completed.
* 1 FETCH (UID 1 FLAGS ())
* 2 FETCH (UID 2 FLAGS ())
* 3 FETCH (UID 3 FLAGS ())
9 OK Fetch completed.
10 OK Store ignored with read-only mailbox.
+ idling
11 OK Idle completed.
12 OK Close completed.
* BYE Logging out
13 OK Logout completed.
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-- 
  Sergey ivanov.