Drupal #limit_validation_errors does not work - drupal

Question

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.
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:
$form['application']['education']['add_education'] = array(
'#type' => 'submit',
'#value' => 'Add',
'#submit' => array('_education_submit'),
'#limit_validation_errors' => array(),
);
The code above doesn't work, the code below works though:
$form['add_education'] = array(
'#type' => 'submit',
'#value' => 'Add',
'#submit' => array('_education_submit'),
'#limit_validation_errors' => array(),
);

Answer 1

It looks like Drupal is looking for the triggering_element using the value attribute to compare; as I have another button with the same value, the system is messing up the values and taking the other button as the clicked one.
To fix the code, I only have had to change the #value property of the button. It was working when I changed the position on the tree because in that case Drupal took the right button.

Answer 2

Here is the example of using this property:
$form['add_education'] = array(
'#type' => 'submit',
'#value' => 'Add',
'#submit' => array('submit_function'),
'#limit_validation_errors' => array(array('_education_submit')),
);

Answer 3

For Drupal 8, I had to switch from a type="submit" to type="button" in order to disable errors + use Ajax.
public function buildForm(array $form, FormStateInterface $form_state) {
// ...
// Create Draft Button
$form['#prefix'] = '<div id="send-emails-manual-send-by-role-wrapper">';
$form['#suffix'] = '</div>';
$form['actions']['save_draft'] = [
'#type' => 'button',
'#value' => $this->t('Save Draft'),
'#name' => 'submit__save_draft', // TODO: Make constant
'#limit_validation_errors' => [],
'#ajax' => [
'callback' => [$this, 'ajaxSubmitForm'],
'wrapper' => 'send-emails-manual-send-by-role-wrapper',
'method' => 'replace',
'effect' => 'fade',
],
];
return $form;
}
/**
* Submit the form using ajax
*/
public function ajaxSubmitForm(array &$form, FormStateInterface $form_state) {
$this->submitForm($form, $form_state);
return $form;
}