How to remove vestigial gmirror device?

[Remo Lacho]

Installed 5.3-Stable from the February ISO Snapshot on an old Pentium Pro
600MH ATX box with 256MB memory and two WD UDMA33 6.4GB drives.

After several false starts with GMirror (guided by Ralf S. Engelschal's
excellent How-To <http://people.freebsd.org/~rse/mirror/>) the system is
now stable and has survived many kernel recompiles without incident.

One problem, one of the original test GMirror devices refused to go away. 
It did not respond to the "remove" or "forget" parameters.

The "deactivate" parameter seemed to do the trick, however, upon boot-up
the following message is generated:

"GEOM_MIRROR: Device gmusr: provider ad4 marked as inactive, skipping."

The "list" parameter does not list the gmusr device as being active.

When "gmirror activate gmusr ad4" is invoked the response is:

"Cannot write metadata from ad4: Operation not permitted.
Not fully done."

Although the vestigial device does not seem to cause any trouble, it is
annoying to get the message at boot-up.

I there a configuration file that can be edited or a specific disk sector
where the device entry can be deleted with a disk editor?

If not, any other way to remove the device permanently other than a system
reinstall.

Thank you.

--
Remo