In the latest version of knfsd the semantic of /etc/exports does not work as before. The NFS export of filesystems across mounting points does not work. For instance, if we have a filesytem with a partition for root (/) one for /usr and another for /home, the export of root / does not export /usr and /home, namely the /usr and /home directory in the mounted filesystem will result empty. Furthermore, trying to export the subdirectories explicitely (/usr, /home) will results in strange behavior and crash of the system.
I believe the semantics of /etc/exports are the same now as with BSD. That is nfs mounts may not spread across partitions.
The mount points need to be exported explicitly.