Help getting vbox .vdi imares to run under Freenas

[Nils]

Hello, I'm fighting to get vbox vdi images to run under FreeNAS and
don't know what else to try. I've filed and commented on these two bugs:
https://github.com/pr1ntf/iohyve/issues/227
https://github.com/pr1ntf/iohyve/issues/228

...but I think the problem is not with bhyve itself or with iohyve, but
either with grub-bhyve or ZFS.
Running installation ISOs etc. works fine, but I need to get the VDIs
going.,

Any pointers are welcome...
Thanks
Nils