validation not working properly with nested form

Hi all,

I have two class
class Person
    include MongoMapper::Document
    one :address
    validates_associated :address

   ... validates for keys
   ... other keys
end

class Address
    include MongoMapper::EmbeddedDocument
    belongs_to :person

   ... validates for keys
   ... other keys
end

And i have the following in my view
<%= form_for(@person) do |f| %>

   .... fields for person

      <%= f.fields_for :address do |address_form| %>
          ... fields for address
      <% end %>
<% end %>

when i click submit button, validation is working for both class, however
only fields in Person class get highlighted, fields for Address class will
NOT highlight.

how can i fixed this?

Thanks