I have submitted bug report https://www.illumos.org/issues/8896 explaining the issues with the changes that were implemented in response to bug https://www.illumos.org/issues/6111 (which were merged to FreeBSD in https://github.com/freebsd/freebsd/commit/7641d40e2f9dde0788597491b388fba03b9869fa#diff-0e9a095472eb326bdbdbbc69b47d7c98). I believe this change should be reverted as per the discussion there. I'm not sure what the process is regarding FreeBSD's version of libzfs, should this wait for the illumos version to be changed, or can it be changed here and pushed back?
Over to committer of r305201.