inheritance model, then uniquenese validation does not work

I have a model V1::Profile::Subnet inheritance from V1::Profile::Base

module V1 
  class Profile::Subnet < V1::Profile::Base
  end
end

base model:

module V1
  class Profile::Base < CouchRest::Model::Base
   use_database $DATABASE_AV_TESTS
   property :name, String
   validates :name,   :presence => {:message => 'cannot be blank, Profile not saved'},
                      :uniqueness => {:message => 'Profile name must be unique, Profile not saved'},
                      :length => {:maximum => 255, :message => 'is too long (maximum is 255 characters)'}
  validates :author, :presence => {:message => 'cannot be blank, Profile not saved'}

  end
end

If I saved two subnet with same name, it didn't complain, if I save a subnet with blank name , it complains, it is wired that validation presence works, but not uniqueness, any one has idea?