Comment 6 for bug 1321335

Now that the bug is confirmed to affect multiple users, allow me to post the work-around I found, in hopes it will help address the issue.

I have installed grub-pc, grub-pc-bin, grub-common, grub2-common version 2.01-22debian1+zfs3-0.6.3-2~wheezy and zfs-initramfs version 0.6.3-0.27~21b446~wheezy, all downloaded manually from the zfsonlinux debian repository, and marked as held (apt-mark hold grub-pc ...).
In addition, I added zfsforce=1 to GRUB_CMDLINE_LINUX in /etc/default/grub (I haven't checked if that's still required after the upgrade to zfs 0.6.3).

Finally, if one uses the root dataset (the one with the pool's name) for the root filesystem instead of a child dataset, one has to remove the trailing slash from the pool name after each update-grub. That's a confirmed issue @ZoL, one for which I do not know if a decision has been made yet.