GEOM hangover disables NFS

On three nodes in my cluster (nodes n17, n18, and n19), I had
GEOM use /dev/ad4s1e for tests with gmirror and ggated/ggatec.
I found that GEOM was insufficient for my needs and decided 
to return the 3 partitions to NFS-exported partitions.  It seems
that once GEOM touches a partition, the partition can no longer
be used by NFS.

I'll illustrute the problem with n17:/dev/ad4s1e.  In what follows,
n10 is the master node.  Both n10 and n17 have brand new worlds
and kernels from about 45 minutes ago.

n10:kargl[203] ssh n17
n17:kargl[201] df
Filesystem        1M-blocks  Used  Avail Capacity  Mounted on
/dev/ad4s1a             247   104    123    46%    /
devfs                     0     0      0   100%    /dev
/dev/ad4s1e          222780     0 204958     0%    /data
/dev/ad4s1d            3962   182   3463     5%    /usr
n10:/home            193947 92855  85576    52%    /home
n10:/usr/local        19832 10494   7750    58%    /usr/local

n17:kargl[202] tail -1 /etc/exports
/data   -alldirs        node10 node21

The above is after a 'newfs -U /dev/ad4s1e' and a reboot.

n10:root[244] ls / | grep -E ^n
n11/ n12/ n13/ n14/ n15/ n16/ n17/ n18/ n19/ n20/ n21/

n10:root[245] mount_nfs -o tcp n17:/data /n17
n10:root[246] mount -v | grep n17
n17:/data on /n17 (nfs, fsid 0eff000303000000)
n10:root[247] ls /n17
ls: /n17: Input/output error
n10:root[248] ls / | grep -E ^n
ls: n17: Input/output error
n11/ n12/ n13/ n14/ n15/ n16/ n18/ n19/ n20/ n21/

n10:root[251] umount /n17
n10:root[252] ls / | grep -E ^n
n11/ n12/ n13/ n14/ n15/ n16/ n17/ n18/ n19/ n20/ n21/

So, how does one exorcise GEOM from /dev/ad4s1e?

-- 
Steve