Cyrus with a NFS storage. random DBERROR

[ram]

I testing cyrus with a NFS storage by two *identical* cyrus + postfix
servers

Both /var/spool/imap and /var/imap are mounted by both servers ( the
socket directory is moved out of the mount) 

Everything seems working fine but I find sometimes dupelim doesnt work.
I tried to  debug , I get errrors like these in my maillog 

DBERROR: skiplist recovery /var/imap/deliver.db: ADD at E2C8 exists

What could be the reason ? 

I am using cyrus-imapd 2.3.7 on centos 4.4  on both servers , with a
NetAPP box for storage

Thanks
Ram