Mount updating busted for ufs2

Looks like mount updating is broken:

% mount
/dev/ad0s4a on / (ufs2, local)
devfs on /dev (devfs, local)
/dev/ad0s4d on /usr (ufs2, local, soft-updates)
/dev/ad0s4e on /cache (ufs2, local, read-only)
/dev/ad0s4f on /dell (ufs2, NFS exported, local, soft-updates)
linprocfs on /usr/compat/linux/proc (linprocfs, local)
procfs on /proc (procfs, local)
% sudo mount -uw /cache
mount: exec mount_ufs2 not found in /sbin:/usr/sbin: No such file or directory
% sudo mount -uw /dev/ad0s4e /cache
%

Anybody have a fix?  This has worked for years.  I shouldn't have to
specify the device name.

Warner