title: Drupal #limit_validation_errors does not work
body: <p>I am constructing a form with Drupal FAPI and is a little bit complex one. What I want to do is to put a button and add some information when the user clicks it, so I need to skip validations with that button. I'm trying to use the #limit_validation_errors property but doesn't seem to work and is executing all validations.</p>
  
  <p>I've noticed that when I put the element at the root level of the form tree it does work. This is what I have:</p>
  
  <pre><code>$form['application']['education']['add_education'] = array(
      '#type' =&gt; 'submit',
      '#value' =&gt; 'Add',
      '#submit' =&gt; array('_education_submit'),
      '#limit_validation_errors' =&gt; array(),
  );
  </code></pre>
  
  <p>The code above doesn't work, the code below works though:</p>
  
  <pre><code>$form['add_education'] = array(
      '#type' =&gt; 'submit',
      '#value' =&gt; 'Add',
      '#submit' =&gt; array('_education_submit'),
      '#limit_validation_errors' =&gt; array(),
  );
  </code></pre>