Kernel doesn't find root from new style partitionable array

Hi,

I'm using the new support for partitioning a normal md-array in 2.6.28
kernel. The devices are created and work just fine:

mika@aeon:~$ ll /dev/md0*
brw-rw---- 1 root disk   9, 0 2009-01-10 18:31 /dev/md0
brw-rw---- 1 root disk 259, 0 2009-01-10 18:31 /dev/md0p1
brw-rw---- 1 root disk 259, 1 2009-01-10 18:31 /dev/md0p2

Using /dev/md0p1 as root device for kernel however doesn't work.

Kernel autodetects the array just fine:

md: Waiting for all devices to be available before autodetect
md: If you don't use raid, use raid=noautodetect
md: Autodetecting RAID arrays.
md: Scanned 1 and added 1 devices.
md: autorun ...
md: considering sda1 ...
md:  adding sda1 ...
md: created md0
md: bind<sda1>
md: running: <sda1>
raid1: raid set md0 active with 1 out of 2 mirrors
md: ... autorun DONE.

But not the partitions, root device is not found and the list of devices
shown only has md0, not the partitions below it.

When booting from another disk I can see that the md0 partitions are
only found later:

 md0: p1 p2

This line shows up after root is already mounted.

I tried booting with the rootwait parameter, but it didn't help.

Attached is dmesg from booting with another disk that shows the md
partitions being detected late.