I encountered not nice behaviour of nfs in -current.
I mounted 3 volumes via nfs:

flam:/		/flam		nfs	ro,noauto		0	0
flam:/stuffy	/flam/stuffy	nfs	ro,noauto,nosuid,nodev	0	0
flam:/volatile	/flam/volatile	nfs	rw,noauto		0	0

flam:/            290799    171643    104617    62%    /flam
flam:/volatile  19689614   8750118   9955016    46%    /flam/volatile
flam:/stuffy   111928190  51431130  54900652    48%    /flam/stuffy

flam:/ on /flam type nfs (read-only)
flam:/volatile on /flam/volatile type nfs
flam:/stuffy on /flam/stuffy type nfs (read-only, nosuid, nodev)

Then flam was rebooted.  After that I still can
access /flam and /flam/volatile.  However /flam/stuffy appears empty.

When I execute showmount -a on flam I receive nothing:

# showmount -a
All mount points on localhost:

When I try to unmount /flam/stuffy I get:

# umount -fv /flam/stuffy
/stuffy: unmount from /flam/stuffy
umount: /flam/stuffy: Invalid argument

# mount -uv /flam/stuffy 
exec: mount_nfs -o update flam:/stuffy /flam/stuffy
mount_nfs: flam:/stuffy on /flam/stuffy: Invalid argument

Despite the fact that /flam/stuffy appears empty I have
open session of xpdf reading book residing on /flam/stuffy,
and I still can read it.