Encode/decode original MBB correctly

The original MBB wasn't encoded/decoded correctly.

Change-Id: Ifeef36509ab8388c6d13c0737ec116633213d92d
Reviewed-on: http://review.couchbase.org/42305
Reviewed-by: Sarath Lakshman <sarath@couchbase.com>
Tested-by: buildbot <build@couchbase.com>