Dovecot 2.2.14 and per user \Seen flags

[Thomas Robers]

Hello,

I have a Dovecot Installation Version 2.2.14 on CentOS 6.5 with shared folder.
UserA shares his INBOX to user UserB. I activated "per user \Seen flags" with

   location = maildir:%%h/Maildir:INDEX=%h/shared/%%u:CONTROL=%h/shared/%%u:INDEXPVT=%h/shared

I think the INDEXPVT setting activates this setting, right?
I activated this setting when there were already several accounts in use. Before we used
shared \Seen flags. But this setting doesn't work on my system. For example UserB marks several
Messages as read in a shared INBOX from UserA and erverything seems alright but then suddenly all
seen Messages are marked as unread again and I see the following error message in the log file:

   Oct 27 14:40:48 mail dovecot: imap(UserB at tutech.de): Error: /export/home/imap/UserB at tutech.de
   /shared/.INBOX/dovecot.index.pvt reset, view is now inconsistent
   Oct 27 14:40:48 mail dovecot: imap(UserB at tutech.de): Disconnected: BUG: Unknown internal error
   in=1020 out=2757

My Dovecot configuration is:

root at mail:~# doveconf -n
# 2.2.14: /etc/dovecot/dovecot.conf
# OS: Linux 2.6.32-431.29.2.el6.x86_64 x86_64 CentOS release 6.5 (Final) ext4
auth_master_user_separator = *
auth_mechanisms = plain login
auth_verbose = yes
disable_plaintext_auth = no
mail_debug = yes
mail_location = maildir:/export/home/imap/%Lu/Maildir
mail_plugins = acl zlib
managesieve_notify_capability = mailto
managesieve_sieve_capability = fileinto reject envelope encoded-character vacation subaddress
comparator-i;ascii-numeric relational regex imap4flags copy include variables body enotify
environment mailbox date ihave duplicate
mbox_write_locks = fcntl
namespace {
  hidden = no
  ignore_on_failure = no
  inbox = no
  list = children
  location = maildir:%%h/Maildir:INDEX=%h/shared/%%u:CONTROL=%h/shared/%%u:INDEXPVT=%h/shared
  prefix = shared/%%u/
  separator = /
  subscriptions = yes
  type = shared
}
namespace inbox {
  hidden = no
  inbox = yes
  list = yes
  location =
  mailbox Drafts {
    special_use = \Drafts
  }
  mailbox Junk {
    special_use = \Junk
  }
  mailbox Sent {
    special_use = \Sent
  }
  mailbox "Sent Messages" {
    special_use = \Sent
  }
  mailbox Trash {
    special_use = \Trash
  }
  prefix = INBOX/
  separator = /
  type = private
}
passdb {
  args = /etc/dovecot/master-users
  driver = passwd-file
  master = yes
}
passdb {
  args = /etc/dovecot/dovecot-ldap.conf.ext
  driver = ldap
}
plugin {
  acl = vfile:/etc/dovecot/global-acls:cache_secs=300
  acl_shared_dict = file:/export/home/shared-db/shared-mailboxes
  mail_log_events = delete undelete expunge copy mailbox_delete mailbox_rename
  mail_log_fields = uid box msgid size
  zlib_save = gz
  zlib_save_level = 6
}
protocols = imap pop3 lmtp sieve
service auth {
  unix_listener /var/spool/postfix/private/auth {
    mode = 0666
  }
  unix_listener auth-userdb {
    group = vmail
    mode = 0660
    user = vmail
  }
}
service imap-login {
  process_limit = 500
  process_min_avail = 20
}
service lmtp {
  inet_listener lmtp {
    address = 127.0.0.1
    port = 24
  }
}
ssl = required
ssl_cert = </etc/pki/dovecot/certs/mail.tutech.de.crt_chain
ssl_key = </etc/pki/dovecot/private/mail.tutech.de.key
ssl_protocols = !SSLv3 !SSLv2
syslog_facility = local6
userdb {
  args = /etc/dovecot/dovecot-ldap-userdb.conf.ext
  driver = ldap
}
protocol lmtp {
  mail_plugins = acl zlib sieve
}
protocol imap {
  mail_plugins = acl zlib imap_zlib imap_acl
}

I don't know, is there something wrong with my configuration, am I
missing sonething?

Any hint would be helpful.

Thank you

Best regards
Thomas