[Dovecot] fs_flush_file_handle_cache_dir: rmdir(/var/mail) AGAIN

We are running Dovecot 2.0.12. It runs on only one server and /var/mail is local where all the INBOX's are stored. Users other IMAP folders are NFS mounted on the server.

We see frequent

Error: nfs_flush_file_handle_cache_dir: rmdir(/var/mail) failed: Device busy

I know this error message has been around a long time. Should we still be seeing it on 2.0.12 with a local /var/mail. Perhaps the message is misleading and really complaining about folders other than INBOX that are NFS mounted.

Our config has

dovecot.conf:mail_nfs_index = no dovecot.conf:mail_nfs_storage = yes

is that correct given the above?

Also, does the flush error messages have any real consequences? My understanding is that the rmdir is meant to fail, just to force a flush.