flexmock error when mocking methods created by method_missing & respond_to_missing?

test_dog_barking.rb

# slight modification of the example 'Creating Partial Mocks' from http://flexmock.rubyforge.org/ 
require 'test/unit'
require 'flexmock/test_unit'

class Woofer
  def woof
    'miau'
  end
end

class Dog
  def initialize
    @woofer = Woofer.new
  end
  def wag
    :happy
  end
  def method_missing(method, *args, &block)
    if method.to_s =~ /bark/
      @woofer.woof
    else
      super
    end
  end
  def respond_to_missing?(method, *)
    method =~ /bark/ || super
  end
end

class TestDogBarking < Test::Unit::TestCase
  include FlexMock::TestCase

  # Setup the tests by mocking the +new+ method of
  # Woofer and return a mock woofer.
  def setup
    @dog = Dog.new
    flexmock(@dog, :bark => :grrr)
  end

  def test_dog
    assert_equal :grrr, @dog.bark   # Mocked Method
    assert_equal :happy, @dog.wag    # Normal Method
  end
end

testoutput.txt

[ruby-1.9.2-p318]$ ruby dog_test.rb
Loaded suite dog_test
Started
E
Finished in 0.001032 seconds.

  1) Error:
test_dog(TestDogBarking):
NameError: undefined method `flexmock_original_behavior_for_bark' for class `Dog'
    /Users/max/.rvm/gems/ruby-1.9.2-p318/gems/flexmock-0.9.0/lib/flexmock/partial_mock.rb:280:in `alias_method'
    /Users/max/.rvm/gems/ruby-1.9.2-p318/gems/flexmock-0.9.0/lib/flexmock/partial_mock.rb:280:in `block in restore_original_definition'
    /Users/max/.rvm/gems/ruby-1.9.2-p318/gems/flexmock-0.9.0/lib/flexmock/partial_mock.rb:279:in `class_eval'
    /Users/max/.rvm/gems/ruby-1.9.2-p318/gems/flexmock-0.9.0/lib/flexmock/partial_mock.rb:279:in `restore_original_definition'
    /Users/max/.rvm/gems/ruby-1.9.2-p318/gems/flexmock-0.9.0/lib/flexmock/partial_mock.rb:162:in `block in flexmock_teardown'
    /Users/max/.rvm/gems/ruby-1.9.2-p318/gems/flexmock-0.9.0/lib/flexmock/partial_mock.rb:160:in `each'
    /Users/max/.rvm/gems/ruby-1.9.2-p318/gems/flexmock-0.9.0/lib/flexmock/partial_mock.rb:160:in `flexmock_teardown'
    /Users/max/.rvm/gems/ruby-1.9.2-p318/gems/flexmock-0.9.0/lib/flexmock/mock_container.rb:53:in `block in flexmock_close'
    /Users/max/.rvm/gems/ruby-1.9.2-p318/gems/flexmock-0.9.0/lib/flexmock/mock_container.rb:52:in `each'
    /Users/max/.rvm/gems/ruby-1.9.2-p318/gems/flexmock-0.9.0/lib/flexmock/mock_container.rb:52:in `flexmock_close'
    /Users/max/.rvm/gems/ruby-1.9.2-p318/gems/flexmock-0.9.0/lib/flexmock/mock_container.rb:34:in `flexmock_teardown'
    /Users/max/.rvm/gems/ruby-1.9.2-p318/gems/flexmock-0.9.0/lib/flexmock/test_unit.rb:26:in `teardown'
    /Users/max/.rvm/gems/ruby-1.9.2-p318/gems/flexmock-0.9.0/lib/flexmock/test_unit_integration.rb:36:in `teardown'

1 tests, 2 assertions, 0 failures, 1 errors, 0 skips

Test run options: --seed 54814

workaround.rb

# lib/flexmock/partial_mock.rb
#
# workaround for the problem:
# ignore NameErrors the same way create_alias_for_existing_method(method_name) does:

def restore_original_definition(method_name)
  begin
    method_def = @method_definitions[method_name]
    if method_def
      the_alias = new_name(method_name)
      sclass.class_eval do
        alias_method(method_name, the_alias)
      end
    end
  rescue NameError => _
    # Alias attempt failed
    nil
  end
end