Can't NFS mount ZFS volume

Both client and server have been upgraded from SVN r324033 to r324089

Now I can't mount a ZFS dataset over NFS :-(

imb_at_toshi:/home/imb> sudo /sbin/mount -t nfs vm01:/usr/local/exports/ /mnt

imb_at_toshi:/home/imb> mount
/dev/ada0s3a on / (ufs, local, soft-updates)
devfs on /dev (devfs, local, multilabel)
procfs on /proc (procfs, local)
linprocfs on /usr/compat/linux/proc (linprocfs, local)
linsysfs on /usr/compat/linux/sys (linsysfs, local)
vm01:/usr/local/exports on /mnt (nfs)

imb_at_toshi:/home/imb> sudo ls -l /mnt
ls: /mnt: Input/output error

The server shows the mount as being registered ..

imb_at_vm01:/home/imb> showmount -a
All mount points on localhost:
toshi.auburn.protected-networks.net:/usr/local/exports

It takes some time to complete an umount request but it does complete,

Any thoughts?

	imb