According to the documentation:
The command mount does not pass the mount options unbindable, runbind-
able, private, rprivate, slave, rslave, shared, rshared, auto, noauto,
comment, x-*, loop, offset and sizelimit to the mount.<suffix> helpers.
All other options are used in a comma-separated list as argument to the
-o option.
So it should not be a problem of mount.nfs.