I just upgraded from a 3.99.7 July 24 kernel to 3.99.9 Oct 14, and it
seems that unionfs is no longer showing the lower filesystem. mount -v
shows:

yerfable:/usr/src on /usr/src type nfs (fsid: 0xb01/0x70b, reads: sync 0 async 0, writes: sync 0 async 0)
<below>:/usr/src on /usr/src.local type union (fsid: 0xc202/0x69c2, reads: sync 0 async 0, writes: sync 0 async 0)

And ls shows:
cheetah /usr/src# ls -F /usr/src
BUILDING        build.sh*       etc/            regress/        usr.bin/
CVS/            crypto/         games/          rescue/         usr.sbin/
Makefile        diff-mc         gnu/            sbin/           x11/
Makefile.inc    dist/           include/        share/
UPDATING        distrib/        lib/            sys/
bin/            doc/            libexec/        tools/
cheetah /usr/src# ls -F /usr/src.local
CVS/            destdir.mac68k/ include/        regress/        usr.bin/
bin/            dist/           lib/            releasedir/     usr.sbin/
build.log       distrib/        libexec/        rescue/         x11/
contrib/        doc/            obj.alpha@      sbin/
crypto/         etc/            obj.amd64@      share/
destdir.alpha/  games/          obj.i386@       sys/
destdir.i386/   gnu/            obj.mac68k@     tools/

This is on amd64, BTW... haven't tried any other ports yet.
-- 
Name: Dave Huang         |  Mammal, mammal / their names are called /
INet: khym@azeotrope.org |  they raise a paw / the bat, the cat /
FurryMUCK: Dahan         |  dolphin and dog / koala bear and hog -- TMBG
Dahan: Hani G Y+C 29 Y++ L+++ W- C++ T++ A+ E+ S++ V++ F- Q+++ P+ B+ PA+ PL++