Lost quota, maildirsize with value S0

[grupodecorreo10 via dovecot]

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