Lost quota, maildirsize with value S0

Hi,We have installed  dovecot 2.2.22. we have servers as director dovecot and servers as dovecot backend. The mailboxes are estored in maildir format, over nfs (Emc Isilon).The problem we have is that sometimes some aleatory users loss her quota and the maildirsze show ilimited cuota, with S0 value in maildirsive file.The mails are stored in the mailboxes with maildrop and postfix, but we have done some test with postfix stoped. Only Dovecot openning the mailbox and the maildirsize is corrupted.I do not known where to look. We have configured dovecot with all the recomendarions for nfs.Thank you