AUTOFS and NFS not playing together nicely

At the risk of being dubbed insane, here goes:

On five FreeBSD 10.1-RELEASE-p9 production servers autofs(5) is enabled
and working as advertised.  On the same servers nfs v3 clients are also
fat, dumb and happy.

On a test server where autofs(5) is also enabled and working well, I am
testing nfs v3 (later v4) server. Strange things are happening.

When nfs mountd(8) is running, the autofs(5) auto-mount (via automountd)
function seems to work, but the autofs(5) auto-unmount (via
autounmountd) never occurs.

Without nfs mountd(8), when the filesystem /disc is auto-mounted (via
autoumountd), the mount(8) command shows status of (ufs, local,
journaled soft-updates, auto-mounted) for the auto-mounted filesystem
and after the autofs(5) timeout period (600 seconds) the filesystem is
auto-unmounted (via autounmountd). No problem.

With nfs mountd(8) the mount(8) command shows (ufs, local, journaled
soft-updates).  The auto-mounted filesystem is never (a long, long time)
unmounted. Big problem.

Without nfs mountd(8) running, the mount(8) command "mount -o
automounted /dev/ada0p8 /disc" mounts the filesystem and the mount(8)
command shows (ufs, local, journaled soft-updates, automounted) for the
manually mounted filesystem and after the autofs(5) timeout period (600
seconds) the filesystem is auto-unmounted even though it was not mounted
automatically.  No problem.

With nfs mountd(8), the mount(8) command "mount -o
automounted /dev/ada0p8 /disc" mounts the filesystem but the mount(8)
command shows (ufs, local, journaled soft-updates) and after the timeout
period (600 seconds) the filesystem is remains mounted.  Big problem.

It appears that nfs mountd(8) is interferring with the mount(8)
command's -o option processing but admittedly that is just a very weak
SWAG.

I have adequate hardware (real and virtual) to do any testing that may
be suggested.  Most days there is no time constraint either.

--------------------------------------------------------
The /etc/auto_master file is two lines:

1:/net	-hosts	-nobrowse,nosuid            (original)

2:/-	/etc/autofs/auto_disc

--------------------------------------------------------
The /etc/autofs/auto_disc file is one line:

1:/disc	-fstype=ufs	:/dev/ada0p8

--------------------------------------------------------

Once again, everything works well when nfs mountd(8) is not present in
the system.

Thanks for any assistance that you may be able to supply.

David Boyd.