Muliple has_one's on a polymorphic association

I wish to add a billing_address and a delivery_address to my Client's.
So i thought i would make my Addresses polymorphic.

class Client < ActiveRecord::Base
  has_many :addresses, as: :addressable
  has_one :delivery_address, class_name: 'Address', as: :addressable
  has_one :billing_address, class_name: 'Address', as: :addressable

  def delivery_address
    super || NullAddress.new
  end

  def billing_address
    super || NullAddress.new
  end
end

class Address < ActiveRecord::Base
  belongs_to :addressable, polymorphic: true

  def full_address
    [line1, line2, town, county, postcode].compact.join(', ')
  end
end

How ever when i try to update the billing address @client.billing_address
both the @client.billing_address and @client.delivery_address get set to the same address. And the previous addresses :addressable_id gets set to nil.

  [1] #<Address:0x007f8bb1acdf20> {
      :addressable_id => nil,
    :addressable_type => "Client",
             :country => "Ireland",
              :county => "Limerick",
          :created_at => Sat, 25 Jun 2016 17:43:48 UTC +00:00,
                  :id => 2,
               :line1 => "123 New Street",
               :line2 => "College Court",
            :postcode => "DTW1234",
                :town => "Limerick",
          :updated_at => Sat, 25 Jun 2016 17:44:46 UTC +00:00
  },
  [2] #<Address:0x007f8bb1ace060> {
      :addressable_id => 25,
    :addressable_type => "Client",
             :country => "Ireland",
              :county => "Limerick",
          :created_at => Sat, 25 Jun 2016 17:44:46 UTC +00:00,
                  :id => 3,
               :line1 => "126 New Street",
               :line2 => "College Court",
            :postcode => "DTW1234",
                :town => "Limerick",
          :updated_at => Sat, 25 Jun 2016 17:58:14 UTC +00:00
  }

]

Obviously I can still see all the addresses doing @client.addresses. But how do I implement and maintain reference to separate billing and delivery address for a client.

Any tips/pointers welcome,
Thanks :)

Hmm, I wonder if you need to include the address ID in the form as a hidden field so Rails knows which records to update. If it doesn't have the ID of the nested model, it is just going to create a new one, so that might be what's happening here. It seems like it's creating new records instead of updating the old ones. Does that sound right?