Odd behaviour for pp with ActiveSupport::OrderedHash

ordered_hash_wtf.rb

# Ruby 1.8.7-p330
# ActiveSupport 3.0.7

require 'rubygems'
require 'active_support/ordered_hash'
require 'pp'

test = ActiveSupport::OrderedHash.new

test[:one]   = 1
test[:two]   = 2
test[:three] = 3

puts test.inspect
# => #<OrderedHash {:two=>2, :three=>3, :one=>1}>
#
# Alright, this seems sensible

pp test
# => {[:one, 1]=>nil, [:two, 2]=>nil, [:three, 3]=>nil}
#
# ... Wait, what?