dovecot - Aug 2007 - index and control files not being created

Hello, I'm configurating dovecot 1.0.3 on debian etch.
While trying to set public folders, y decided to have the index and 
control files on the users homes. those homes are mounted by nfs, with 
disabled access to root.
In that scenario, I'm getting the errors i transcribe next:

Aug 16 11:21:17 server dovecot: IMAP(user): 
fchown(/home/user/Maildir/shared-settings/control/.folder/dovecot-uidlis
t) failed: Operation not permitted
Aug 16 11:21:17 server dovecot: IMAP(user): 
fchown(/home/user/Maildir/shared-settings/control/.folder/dovecot-uidlis
t) failed: Operation not permitted
Aug 16 11:21:17 server dovecot: IMAP(user): 
rename(/inbox/shared/.folder/cur/mailfile, 
/inbox/shared/.folder/cur/mailfile
:2,S) failed: Operation not permitted
Aug 16 11:21:17 server dovecot: IMAP(user): 
fchown(/home/user/Maildir/shared-settings/control/.folder/dovecot-uidlis
t) failed: Operation not permitted
Aug 16 11:21:17 server dovecot: IMAP(user): 
rename(/inbox/shared/.folder/cur/mailfile, 
/inbox/shared/.folder/cur/mailfile
:2,S) failed: Operation not permitted
Aug 16 11:21:26 server dovecot: IMAP(user): Disconnected: Logged out
Aug 16 11:21:27 server dovecot: IMAP(user): 
fchown(/home/user/Maildir/shared-settings/control/.folder/dovecot-uidlis
t) failed: Operation not permitted
Aug 16 11:21:27 server dovecot: IMAP(user): 
rename(/inbox/shared/.folder/cur/mailfile, 
/inbox/shared/.folder/cur/mailfile
:2,S) failed: Operation not permitted

Then I touched those files and the errors faded away.
Beside that, I was testing the setup, and while trying to delete some 
files on the shared folder, I got another error:
Aug 16 16:38:04 server dovecot: IMAP(user): 
rename(/inbox/shared/.folder/cur/1183976419.755_0.server:2,Sa, 
/inbox/shared/.folder/cur/1183976419.755_0.server:2,STa) failed: 
Operation not permitted
Aug 16 16:38:11 server dovecot: IMAP(user): 
fchown(/home/user/Maildir/shared-settings/control/.folder/dovecot-uidlist) 
failed: Operation not permitted
Aug 16 16:38:11 server dovecot: IMAP(user): 
rename(/inbox/shared/.folder/cur/1183976419.755_0.server:2,Sa, 
/inbox/shared/.folder/cur/1183976419.755_0.server:2,STa) failed: 
Operation not permitted

Which seems odd, because I though that  as a flag,  the deleted flag 
should be marked on the index files and not directly on the shared  
folder (where the user hasn't any permission other than reading), ant 
the same goes to the "read" flag

Am I wrong? Is there any workaround to make dovecot behave the way I'd 
liked?

The config follows:

login_executable: /usr/lib/dovecot/imap-login
mail_extra_groups: mail
mail_location: maildir:/home/%u/Maildir:INBOX=/inbox/mdir/%u
mmap_disable: yes
namespace:
  type: private
  separator: /
  location: maildir:~/Maildir:INBOX=/inbox/mdir/%u
  inbox: yes
namespace:
  type: public
  separator: /
  prefix: Shared folders/
  location: 
maildir:/inbox/shared:INDEX=/home/%u/Maildir/shared-settings/index:CONTROL=/home/%u/Maildir/shared-settings/control
auth default:
  passdb:
    driver: passwd
    args: blocking=yes
  passdb:
    driver: shadow
  userdb:
    driver: passwd

Cheers,
Luis