title: Save Ajax response in Magento block html cache
body: <p>For this particular Magento EE site, I've got a controller that creates a block and returns it via Ajax.</p>
  
  <pre><code>$this-&gt;loadLayout();
  $block = $this-&gt;getLayout()-&gt;createBlock('catalog/product_list_related','catalog.product.related')-&gt;setTemplate(...
  $this-&gt;getResponse()-&gt;setBody($block-&gt;toHtml());
  </code></pre>
  
  <p>Simple enough.  I'd like to cache the response with the key being SKU - CUSTOMER GROUP - DATE.  I've put the appropriate methods in the block for setting key, tags and lifetime. All good.</p>
  
  <p>However, nothing is saved to the cache.  </p>
  
  <p>I figured, since it's an EE site, that the Enterprise_PageCache placeholders were blocking it.  But even after removing those, it's not saving.</p>
  
  <p>I've been digging through app/code/core/Mage/Core/Block/Abstract.php to see what's going on.  But I thought I'd check if there were any known "gotchas" with caching a block set by createBlock in controller.</p>
  
  <p>Thanks!
  Wilson</p>