ZFS: invalid zap_type=134218628

I've got following error after upgrading my 9.0-RC1 to RC2 using source and
got this error at loader prompt:

ZFS: invalid zap_type=134218628

when I tried zfsboottest from 9.0-STABLE it failed
./zfsboottest /boot/kernel/kernel /dev/ada0p4
returns pool status correctly but ends with the same message

zfsboottest from 10.0-CURRENT returns pool status, zfsboottest.sh zroot
printed OK message at the end
(very useful zfsboottest.sh wasn't yet merged from current to stable).
I've installed gptzfsboot, zfsloader, loader from -CURRENT and it boots
fine.

I'm running ZFS on GPT partitions, zfs version 28 with dedup on.
File system can be successfully mount using FreeBSD memstick.

I think that patches for boot should be merged to 9.0-RELEASE otherwise
users may have the same problems I had.

best regards,