[Dovecot] no bookeeping using public folders

[Claude Frantz]

Using dovecot 1.0.10. In the config:

namespace public {
      separator = /
      hidden = no
      prefix = Flock/
      location = 
maildir:/home/baratin/PublicMaildir:CONTROL=~/Maildir/control/Flock:INDEX=/var/dovecot/index/%u/Flock
}

This should be a public mail folder owned by "baratin", "read only" for 
all other users. Every user has his/her own control and index area 
related to this public folder. I have verified, they are owner and 
"group" of the respective control and index area.

The problem, while using Thunderbird: The "read only" user can delete 
messages or mark then read. But after a new session, all the messages 
are still "new". Of course, only "baratin" is the owner.

The problem, while using mutt and IMAP: mutt refuse to change any flag 
because the folder is "read only". Of course, this is correct.

My question: Why is no bookkeeping maintained for "other" users, 
although every one has his/her own control and index structure ?

Thanks a lot !

Claude