No ZFS when loading modules from loeader prompt

At the moment, the most recent kernel of FreeBSD 10.0-CURRENT crashes on
all of the boxes I compiled the most recent kernel sources (build a
world ncluding kernel, not only the kernel, so the system is "consistent").

At the loader prompt, I need to unload the buggy kernel and load the old
working one via

load /boot/kernel.old/kernel

Then I load also the ZFS related modules

load /boot/kernel.old/opensolaris.ko
load /boot/kernel.old/zfs.ko

Issuing boot at the end of that stage boots the kernel - the old one
-successfully - but there is no working ZFS and no ZFS volume gets
mounted although the rc.conf is executed correctly.

What am I doing wrong at that point? Why isn't ZFS run and mount properly?

Luckily, just booting the old kernel via load /boot/kernel.old/kernel
and booting it having zfs_enable="YES" in /etc/rc.conf set loads the
/boot/kernel/opensolaris/zfs stuff - usually those kernel modules are
out of sync compared to kernel.old but in this case its just a
coincidence that this works.

So, what is the proper way to have ZFS mounted in an emergency case when
I'm in need of loading a working kernel manually?

Regards,
Oliver