belongs_to validating presence of foreign key

I've recently read
and I seem to be experiencing conflicting behavior with Rails 1.2.3

Parent Table:
id Integer
name String

Child Table:
id Integer
name String
parent_id Integer

class Parent < ActiveRecord::Base
  has_many :children

class Child < ActiveRecord::Base
  belongs_to :parent
  validates_presence_of :parent_id

So from reading the link above, as well as the warning on
I figured this would work.

parent = => "Dad")
child = => "Son")!

However I consistently get "ActiveRecord::RecordInvalid: Validation
failed: Children is invalid"

This behavior is exhibited with both "validates_presence_of :parent"
and ":parent_id"

However, if I remove the "validates_presence_of :parent_id" both
elements are saved and the Child has been saved with the parent id

Am I mis-reading something, or did this work in previous versions?

Running on Intel Mac, against both SQLite3 and MySQL.