Enumerable doesn't wrap objects properly

class A
  include Enumerable

  def initialize
    @hash = {:a => [1], :b => [2,3]}
  end

  def order
    [:a, :b]
  end

  def each
    order.each { |k| yield( k,@hash[k] ) }
    self
  end
end

A.new.each     {|x, y| puts [x, y].inspect }
A.new.map.each {|x, y| puts [x, y].inspect }

# Expected output, seen on jruby1.8 and MRI1.9.2
# [:a, [1]]
# [:b, [2, 3]]
# [:a, [1]]
# [:b, [2, 3]]

# jruby1.9 output, last two lines are wrong
# [:a, [1]]
# [:b, [2, 3]]
# [:a, nil]
# [:b, nil]