title: Rails partial caching is showing view changes despite no model changes
body: <p>Following the guide from "Agile Web Development with Rails 4."
  It covers caching for a product catalog to only re-render products that changed.</p>
  
  <p>I edited (config/environments/development.rb):</p>
  
  <pre><code>config.action_controller.perform_caching = true
  </code></pre>
  
  <p>Added code to return most recently updated product:
  (app/models/product.rb)</p>
  
  <pre><code>def self.latest
    Product.order(:updated_at).latest
  end
  </code></pre>
  
  <p>Lastly updated the store index for the cache:
  (app/views/store/index.html.erb)</p>
  
  <pre><code>&lt;h1&gt;Your Pragmatic Catalog&lt;/h1&gt;
  &lt;% cache ['store', Product.latest] do %&gt;
    &lt;% @products.each do |product| %&gt;
      &lt;% cache ['entry', product] do %&gt;
        &lt;div class="entry"&gt;
          &lt;%= image_tag(product.image_url) %&gt;
          &lt;h3&gt;&lt;%= product.title %&gt;&lt;/h3&gt;
          &lt;%= sanitize(product.description) %&gt;
          &lt;div class="price_line"&gt;
            &lt;span class="price"&gt;&lt;%= number_to_currency(product.price) %&gt;&lt;/span&gt;
          &lt;/div&gt;
        &lt;/div&gt;
      &lt;% end %&gt;
    &lt;% end %&gt;
  &lt;% end %&gt;
  </code></pre>
  
  <p>The book states the only way to test if caching is working is to change the view so all I did was add some lorem ipsum within one or both cache tags but the browser immediately shows the change on refresh... Frustrating! Any clue?</p>