How to duplicate a pool with zfs send/recv without breaking mountpoints?

I'll let the output speak for itself. This is after running
zpool create slave X && zfs create slave/received && NOW=$(date  
+"backup-%Y%m%d-%H%M"); zfs snapshot -r tank_at_$NOW && zfs send -R tank_at_ 
$NOW | zfs recv -vFd slave/received && zpool export slave && zpool  
import slave

[root_at_chaos ~]# mount
tank/root on / (zfs, local, noatime)
devfs on /dev (devfs, local)
/dev/ad0s1a on /bootdir (ufs, local, soft-updates)
tank/tmp on /tmp (zfs, local, noatime)
tank/usr on /usr (zfs, local, noatime)
tank/usr/ports on /usr/ports (zfs, local, noatime)
tank/usr/ports/distfiles on /usr/ports/distfiles (zfs, local, noatime)
tank/usr/src on /usr/src (zfs, local, noatime)
tank/var on /var (zfs, local, noatime)
//SERENITY_at_EXSCAPE/FBSDBACKUP on /mnt/backup (smbfs)
slave/received/root on / (zfs, local, noatime)
slave on /slave (zfs, local)
slave/received/tmp on /tmp (zfs, local, noatime)
slave/received/usr on /usr (zfs, local, noatime)
slave/received/usr/ports on /usr/ports (zfs, local, noatime)
slave/received/usr/ports/distfiles on /usr/ports/distfiles (zfs,  
local, noatime)
slave/received/usr/src on /usr/src (zfs, local, noatime)
slave/received/var on /var (zfs, local, noatime)
[root_at_chaos ~]# ls /dev
[root_at_chaos ~]# zfs list
internal error: failed to initialize ZFS library (shocking!)

Any ideas? I tried setting the mountpoint property on the slave, but  
I'm pretty sure that didn't help (as the next (incremental) backup  
resets the mountpoints to /... again, I suppose).

Regards,
Thomas