title: Wordpress tax_query "and" operator not functioning as expected
body: <p>I have a custom post type of <strong>image</strong> with a custom taxonomy called <strong>image_tag</strong> (it's hierarchical like categories). Here are some examples of the tags that might be used:</p>
  
  <pre><code>Structure (id: 25)
  - House (id: 56)
  - Skyscraper
  Nature
  - Animal
  - Plant (id: 41)
  </code></pre>
  
  <p>So, I want to drill down through the images by selecting multiple tags in conjunction with the "and" operator. For example, finding all photos with <strong>plant</strong>s and <strong>house</strong>s.</p>
  
  <pre><code>$query_args = array(
    'post_type' =&gt; 'image',
    'tax_query' =&gt; array(
      array(
        'taxonomy' =&gt; 'image_tag',
        'terms' =&gt; array(41, 56),    // IDs of "plant" and "house"
        'operator' =&gt; 'and',
      ),
    ),
  );
  </code></pre>
  
  <p>That works fine, the problem begins when I try to include the parent terms, for example:</p>
  
  <pre><code>$query_args = array(
    'post_type' =&gt; 'image',
    'tax_query' =&gt; array(
      array(
        'taxonomy' =&gt; 'image_tag',
        'terms' =&gt; array(25, 41),    // IDs of "structure" and "plant"
        'operator' =&gt; 'and',
      ),
    ),
  );
  </code></pre>
  
  <p>Then I get no results. I'm guessing that because I'm using the "and" operator, Wordpress doesn't include the children of the "Structure" term. Does anyone have an idea how I can get this to work?</p>