geom_mirror for root partition, not possible on recent CURRENT?

I decided to play around with geom_mirror to see if it is anything I could
use on one of my servers. After installing 5.4-RC4 and hooking it up to
mirror the entire disk (mostly following the process described at
http://dannyman.toldme.com/2005/01/24/freebsd-howto-gmirror-system/) I went
ahead and cvsuped the latest CURRENT (2005.05.07.01.00.00) and rebuilt the
system.

After installing the new CURRENT kernel, the system is unable to find the
geom_mirror device during boot (old 5.4-RC4 kernel finds it just fine). The
difference is in the details I guess:

5.4-RC4:
--------
...
GEOM_MIRROR: Device gm0 created (id=1741615369).
GEOM_MIRROR: Device gm0: provider da0 detected.
GEOM_MIRROR: Device gm0: provider da1 detected.
GEOM_MIRROR: Device gm0: provider da1 activated.
GEOM_MIRROR: Device gm0: provider da0 activated.
GEOM_MIRROR: Device gm0: provider mirror/gm0 launched.
Mounting root from ufs:/dev/mirror/gm0s1a

6-CURRENT:
----------
...
GEOM_MIRROR: Device gm0 created (id=1741615369).
GEOM_MIRROR: Device gm0: provider da0 detected.
GEOM_MIRROR: Device gm0: provider da1 detected.
Trying to mount root from ufs:/dev/mirror/gm0s1a

Manual root filesystem specification:
...

mountroot> ?

List of GEOM managed disk devices:
  da1 da0


To me it looks like gmirror never gets around to activating and launching
the mirror under CURRENT. Booting with verbose logging adds no output to the
6-CURRENT case. Am I missing some critical step needed to get gmirror
working on CURRENT that isn't needed on STABLE?

/Daniel Eriksson