zfsloader failure with r239244

Hi,

I just upgraded my system from r238261 to r239244 and was unable to boot
one of my zfs root systems. I had to recover using the zfsloader.old
that is kept in /boot. The messages from zfsloader were:

ZFS: can't find pool by guid
ZFS: can't find pool by guid

can't load 'kernel'

followed by a loader prompt. My loader.conf has:

vfs.root.mountfrom="zfs:zroot"

as well as other settings.

I suspect this may be related to the fact that my zfs root is "formatted
using a legacy on-disk format." Specifically, it is version 14 and for
the record it's on an MBR partition. This system also has two other
pools, one which is version 28 and another which is the latest zpool
version (I think? No version number is shown in "zpool list -o all",
only a "-"). I've avoided zpool upgrading this pool because I'm a little
nervous about updating zfsboot via dd.

I didn't see the issue on another zfs root system which is using GPT and
the latest zpool version and was upgraded from/to the same versions.

Any ideas if this is a bug or something wrong with my system would be
appreciated.

Thanks,
Steve