accepts_nested_attributes_for and has_one

Hi all, I'm seeing some unexpected behaviour in a nested model and I'm
not sure if it's a bug or if I'm doing something wrong. When
assigning nested attributes, the associated object gets replaced with
a new record.

Example code:

class Car < ActiveRecord::Base
  belongs_to :driver
end

class Car < ActiveRecord::Base
  belongs_to :driver
end

Here's some console output:
(pastie version: http://pastie.org/538782)

d = Driver.create :name => "Homer", :age => 40

=> #<Driver id: 1, name: "Homer", age: 40, created_at: "2009-07-08
16:54:44", updated_at: "2009-07-08 16:54:44">

d.create_car :make => "Porshce", :model => "911"

=> #<Car id: 1, driver_id: 1, make: "Porshce", model: "911",
created_at: "2009-07-08 16:55:26", updated_at: "2009-07-08 16:55:26">

d.new_record?

=> false

d.car.new_record?

=> false

d.car.id

=> 1

d.car.attributes

=> {"model"=>"911", "driver_id"=>1, "created_at"=>Wed Jul 08 16:55:26
UTC 2009, "updated_at"=>Wed Jul 08 16:55:26 UTC 2009, "id"=>1,
"make"=>"Porshce"}

attrs = {:car_attributes => {:model => "Boxster"}}

=> {:car_attributes=>{:model=>"Boxster"}}

d.attributes = attrs

=> {:car_attributes=>{:model=>"Boxster"}}

d.car.attributes

=> {"model"=>"Boxster", "driver_id"=>1, "created_at"=>nil,
"updated_at"=>nil, "make"=>nil}

d.car.id

=> nil

d.car.new_record?

=> true

any ideas?