devfs_set_ruleset doesn't seem to like jail_cvs_devfs_ruleset="4"

Trying to setup a jail'd cvs, I came across the jail_cvs_devfs_ruleset
variable for /etc/rc.conf. Running /etc/rc.d/jail start, I get:

/etc/rc.d/jail: DEBUG: found ruleset: devfsrules_jail=4
/etc/rc.d/jail: DEBUG: adding rule (add include $devfsrules_hide_all)
/etc/rc.d/jail: DEBUG: adding rule (add include $devfsrules_unhide_basic)
/etc/rc.d/jail: DEBUG: adding rule (add include $devfsrules_unhide_login)
/etc/rc.d/jail: DEBUG: devfs_init_rulesets: devfs rulesets initialized
/etc/rc.d/jail: DEBUG: devfs_domount(): mount-point is (/var/jail/172.16.1.1/dev), ruleset is (4)
/etc/rc.d/jail: DEBUG: devfs_init_rulesets: devfs rulesets already initialized
/etc/rc.d/jail: WARNING: devfs_set_ruleset: you must specify a ruleset number

I don't know much about shell scripting, but it seems that line 1169
of /etc/rc.subr seems to be resetting the rs variable from 4 to an empty
string:

  [ -n "$1" ] && eval rs=\$$1 || rs=

Since I don't know what eval rs=\$$1 is suppose to be doing, I removed
it. Now, with:

  [ -n "$1" ] || rs=

I get:

/etc/rc.d/jail: DEBUG: found ruleset: devfsrules_jail=4
/etc/rc.d/jail: DEBUG: adding rule (add include $devfsrules_hide_all)
/etc/rc.d/jail: DEBUG: adding rule (add include
$devfsrules_unhide_basic)
/etc/rc.d/jail: DEBUG: adding rule (add include
$devfsrules_unhide_login)
/etc/rc.d/jail: DEBUG: devfs_init_rulesets: devfs rulesets initialized
/etc/rc.d/jail: DEBUG: devfs_domount(): mount-point is
(/var/jail/172.16.1.1/dev), ruleset is (4)
/etc/rc.d/jail: DEBUG: devfs_init_rulesets: devfs rulesets already
initialized
/etc/rc.d/jail: DEBUG: devfs_set_ruleset: setting ruleset (4) on
mount-point (/var/jail/172.16.1.1/dev)


Yet when I do a listing of /var/jail/172.16.1.1/dev, it still lists all
the devices, none are hidden. Any suggestions as to what's going on, and
why rule #4 (copied /etc/defaults/devfs.conf to /etc/devfs.conf) doesn't
seem to be applied?