new submit button to node form not displayed?
It will be displayed somewhere between the node form elements. May be you didn't notice that. Try appending this form element under actions like this. Then You can see the button along with save and preview button.


$form['actions']['submit_delegate'] = array(
  '#type' => 'submit', // I tried also '#type' => 'button'
  '#value' => t('Delegate'),
  '#submit' => array('MYMODULE_form_submit_article_delegate'),
);