Question regarding mmap on ZFS, or possibly Dovecot

I still get massive file corruption when allowing Dovecot to run win 
mmap enabled on ZFS/FreeBSD RELENG_7 (as of one week ago), and I have 
seen symptoms of corruption with Samba and mmap on ZFS (although I 
cannot say with certainty that those samba files were corrupted in the 
FreeBSD end, they may have been mangled by my less-than-trustworthy 
windows).

For dovecot+mmap+zfs I get a googlefull of results, same with 
samba+mmap+zfs.

The question remains the same, however. Is this a problem with 
samba/dovecot using mmap incorrectly, a problem with ZFS as such, or a 
problem with the FreeBSD implementation of ZFS? I'm not asking this to 
have someone to point fingers at, but because I want to do some 
risk-reducing activities. If the problem is in the applications, 
disabling mmap in those applications will be a workaround. If the 
problem is with ZFS itself, or with FreeBSD, things start to get 
interesting (it would need some global switch to turn mmap off, and I'm 
not sure such a thing is practical/possible).

The system running my ZFS is an Athlon64 running amd64 kernel, 4gb ram, 
and a raidZ of 3 500gb samsung disks (on an nForce430 chipset)

//Svein