GEOM_CONCAT odd behaviour

[John]

Hello -stable,

I made a concatenated disk with the gconcat program and compiled
options     GEOM_CONCAT 
into the kernel. When I reboot, this appears in the dmesg:

GEOM_CONCAT: Device data created (id=1971778810).
GEOM_CONCAT: Disk diskid/DISK-WD-WCC130881133 attached to data.
GEOM_CONCAT: Disk diskid/DISK-WD-WCC131034794 attached to data.
GEOM_CONCAT: Disk diskid/DISK-WD-WCC131035892 attached to data.
GEOM_CONCAT: Device concat/data activated.
GEOM_CONCAT: Cannot add disk ada3 to data (error=17).
GEOM_CONCAT: Cannot add disk ada2 to data (error=17).
GEOM_CONCAT: Cannot add disk ada1 to data (error=17).

I tried to run gconcat status which returned something like
'unavailable' (forget the exact error but it suggested the driver wasn't
loaded) so I loaded the kernel module instead ( geom_concat.ko ) 
and now status returns:

[root@ ~]# gconcat status
Name  Status  Components
concat/data      UP  diskid/DISK-WD-WCC130881133
                     diskid/DISK-WD-WCC131034794
                     diskid/DISK-WD-WCC131035892

...so why does it work the second way and not the first? Is compiling it
into the kernel depreciated? This is on PC-BSD 10 but I don't think this
is specific to that branch. The version is 10.0-RELEASE-p4.

thanks,
-- 
John