title: get_posts dont work with post__in
body: <pre><code>$lessons_id = get_post_meta( $post-&gt;ID, '_course-lessons-1', true );
  $posts = get_posts( array( 'post_type' =&gt; 'courses', 'post__in' =&gt; array( $lessons_id ) ) );
  foreach ($posts as $post) : setup_postdata( $post );
  echo get_the_title();
  endforeach;
  wp_reset_postdata();
  </code></pre>
  
  <p>If you put the variable in post__in does not work, it only returns the first value. But getting <code>'post__in' =&gt; array (985,987,254)</code> works. I already echoed the variable, and the output is exactly the same as 985,987,254.</p>
  
  <p>Can you help?</p>