factory_girl_bug.rb

require 'rubygems'
require 'factory_girl'

class Foo
  attr_accessor :bar
end

FactoryGirl.define do
  factory :foo do
    bar [1,2,3]
  end
end

a = FactoryGirl.build(:foo)
p a.bar
#[1, 2, 3]
a.bar << 4

b = FactoryGirl.build(:foo)
p b.bar
#[1, 2, 3, 4]