Unable to boot from zfsroot 9.0-RC2 (while 9.0-RC1 boots fine)

Hi!

I'm having troubles booting today's 9.0-RC2 from zfsroot, I'm getting 'unknown filesystem' error.
But  9.0-RC1 from Tue Nov  8 2011 boots fine.

Here is output with 9.0-RC1 kernel:

# zpool list
NAME    SIZE  ALLOC   FREE    CAP  DEDUP  HEALTH  ALTROOT
zroot  5.97G  2.85G  3.11G    47%  1.00x  ONLINE  -


# zfs list
NAME                      USED  AVAIL  REFER  MOUNTPOINT
zroot                    2.85G  3.02G  2.85G  legacy

# cat /boot/loader.conf 
zfs_load="YES"
vfs.root.mountfrom="zfs:zroot"

Originally that box with installed with FreeBSD 8.x, but continuously updated up to today's version, so :

VER  FILESYSTEM
---  ------------
 4   zroot

VER  POOL
---  ------------
15   zroot


Any suggestions ? What could be the problem?