mmap_disable=yes not honored always

[Peter Benko]

<Sorry for the resend, it seems that the formatting of my original mail got garbled>

Hi all,
 
I'm experimenting with having the mail store on a 9p file system that lacks mmap() functionality. So I disabled it in dovecot:
 
mmap_disable = yes
 
However, I keep getting the following error messages in my log:
 
Oct 15 16:55:00 computer-name dovecot: imap user at domain.com[192.168.1.3] Error: mmap() failed with file /mail/mailboxes/domain.com/user/indexpvt-accounts/other-user/mailboxes/INBOX/dovecot.index.pvt.log: Invalid argument
 
I only get those messages for the shared folder's private indexes. This setup works perfectly on an ext2/3/4 fs.
 
Any opinions, is this a bug? Is mmap_disable not mandatory for all operations?
 
Best regards,
 
Peter