Inconsistent REST behavior

Has anyone seen Rails save nested associations despite their being invalid?

If I hit the site from a different Rails app (using ActiveResource) and try to update the record so that the username is too short it fails (as I expect) and adds an errors attribute to the object that I can inspect. The original account (and associated user and email objects) is unaffected, as I'd expect.

Hitting the same exact URL with a raw HTTP/REST client and sending in XML:

<?xml version="1.0" encoding="UTF-8"?> <account>   <id>1</id>   <user>     <birthdate>2010-01-05</birthdate>     <username>soto</username>   </user>   <email>     <address></address>     <opt-in>true</opt-

    <opt-in-ch1>false</opt-in-ch1>   </email> </account>

It gives me the expected 422 Unprocessible Entity error, which I expect. However it also saves user down as a null! That I do not expect.

My question is why does it correctly handle errors with ActiveResource (eg. doesn't save anything down since their are validation problems) but with a raw PUT request it saves with a null user object (effectively killing the user).

# models

class User < ActiveRecord::Base   belongs_to :account

  validates_length_of :username, :minimum => 6


class Account < ActiveRecord::Base

  has_one :user   has_one :email

  has_many :account_entitlements   has_many :entitlements, :through => :account_entitlements

  accepts_nested_attributes_for :user, :email

  def user=(params)     update_attributes(:user_attributes => params)   end

  def email=(params)     update_attributes(:email_attributes => params)   end


# controller

  def update     @account = Account.find(params[:id])

    respond_to do |format|       if @account.update_attributes(params[:account])         flash[:notice] = 'Account was successfully updated.'         format.html { redirect_to(@account) }         format.xml { head :ok }       else         format.html { render :action => "edit" }         format.xml { render :xml => @account.errors, :status => :unprocessable_entity }       end     end   end