Can't export using nfs4

[Paride Legovini]

Hello, I hope this is the right place where to ask for help about this
issue. I'm playing with nfs4 but with no luck, the system is set up in
the following way.

The kernel (8.0-STABLE) is built with:

options NFSD
options NFSCL

The relevant part of rc.conf is:

# grep nfs /etc/rc.conf
nfs_server_enable="YES"
nfsv4_server_enable="YES"
nfsuserd_enable="YES"
nfs_client_enable="YES"

Then I have a couple of trivial exports:

# cat /etc/exports
V4: /usr
/home

(No, you can't reach them from the Internet!)
Finally I set up /var/db/nfs-stablerestart as explained in nfsv4(4).

Everything works fine for /home, but /usr doesn't get exported at all.
In fact:

# showmount -e
Exports list on localhost:
/home                              Everyone

and the same evidence is given by mount:

/dev/ada0s1f on /usr (ufs, local, noatime, soft-updates)
/dev/ada0s1g on /home (ufs, NFS exported, local, noatime, soft-updates)

(/home is not 'NFS exported'.)

There's nothing relevant in the dmesg on in /var/log/messages.

Any suggestion?

Thank you!
Paride