title: WP_Query order by meta returns 0 results
body: <p>I'm trying to order posts by a meta value which is a date field but I keep getting 0 results. I've tested that there is data by querying without the meta order by.</p>
  
  <pre><code>$args = array(
                  'post_type'  =&gt; 'lp-reviews',
                  'p'          =&gt; $review_id,
                  'post_status'   =&gt; 'publish',
                  'meta_key' =&gt; 'job_completion_date',
                  'meta_type' =&gt; 'date',
                  'orderby' =&gt; 'meta_value',
                  'order' =&gt; 'DESC'
              );
  </code></pre>
  
  <p>Am I missing anything obvious?</p>