Crud many-to-many save issue - edit method + request data

gistfile1.txt

/**
 * Method: edit
 *
 * Amend user entity before save
 *
 * {@inheritDoc}
 */
public function edit($id)
{
    if ($this->request->is('put')) {
        debug($this->request->getData());
        die;
    }
    // set dirty password false when empty
    $this->Crud->on('beforeSave', function (Event $event) {
        if (empty($event->getSubject()->entity->password)) {
            $event->getSubject()->entity->setDirty('password', false);
        }
    });

    return $this->Crud->execute();
}

// Request data debug
[
	'email' => 'okon.curtis@botsford.biz',
	'first_name' => 'Vladimir',
	'last_name' => 'Rowe',
	'roles' => [
		'_ids' => [
			(int) 0 => '2',
			(int) 1 => '1',
			(int) 2 => '3',
			(int) 3 => '6'
		]
	],
	'tags' => '',
	'status' => '1',
	'password' => ''
]