Panic during devfs ruleset operations on 6.0

I'm getting the following on multiple 6.0 machines (UP and SMP):

panic: ruleset 10 already running
db> wh 3747
Tracing pid 3747 tid 100279 td 0xc5d80300
kdb_enter(c08fffa1,1,c08f93ee,ea2cfb58,c5d80300) at kdb_enter+0x30
panic(c08f93ee,a,3,8002440b,c5b666c0) at panic+0x13d
devfs_ruleset_applydm(cc0d3820,cb22fa00,0,c5d80300,cb22fa00) at devfs_ruleset_applydm+0x29
devfs_rules_ioctl(c5c2c400,8002440b,c5b666c0,c5d80300,c095cd80) at devfs_rules_ioctl+0x45a
devfs_rioctl(ea2cfbf0,c0927fa3,c08161eb,c8b91660,0) at devfs_rioctl+0x90
VOP_IOCTL_APV(c095cd80,ea2cfbf0,ea2cfc47,ea2cfc48,c09ad320) at VOP_IOCTL_APV+0xc4
vn_ioctl(cb933990,8002440b,c5b666c0,cc047680,c5d80300) at vn_ioctl+0x18f
ioctl(c5d80300,ea2cfd04,c,28102000,3) at ioctl+0x45d
syscall(3b,3b,3b,bfbfdf58,bfbfe0f1) at syscall+0x2a2
Xint0x80_syscall() at Xint0x80_syscall+0x1f
--- syscall (54, FreeBSD ELF32, ioctl), eip = 0x280c007f, esp = 0xbfbfdeac, ebp = 0xbfbfdec8 ---

It comes from running the following operations:

        mount -t devfs foo ${chroot}/dev
        devfs -m ${chroot}/dev ruleset 10
        devfs -m ${chroot}/dev rule add path 'md*' hide
        devfs -m ${chroot}/dev rule applyset

These devfs operations are needed to work around another devfs panic,
which occurs when device nodes are removed from inside a devfs mount
at the same time the devfs is unmounted.

This panic is going to be very disruptive for the 6.0 package builds
until it can be fixed.

Kris