using touch on a parent model prevents counter_cache from working

Given the following code

Class Topic
  has_many :posts
end

Class Post
  belongs_to :topic, :counter_cache => true

  after_create :touch_topic

  def touch_topic
    self.topic.touch
  end
end

The touch action in the after_create prevents the counter_cache from incrementing the :posts_count on the topic when a post is created. Commenting out the self.topic.touch lets counter_cache work again.