After doing some research I tried using HelperList instead of HelperForm and the toolbar buttons do appear but at the list header, instead of the green area.
On the other hand, HelperForm provides a "buttons" array (I'm not sure if that is a Prestashop 1.6 change or it was there on the 1.5.x versions) which appear left to the submit button in a sort of toolbar below the form.
$this->fields_form[0]['form'] = array(
'tinymce' => true,
'legend' => array(
'title' => $this->l('New test block'),
),
'input' => array(
array(
'type' => 'textarea',
'label' => $this->l('Text'),
'lang' => true,
'name' => 'text',
'cols' => 40,
'rows' => 10,
'class' => 'rte',
'autoload_rte' => true,
)
),
'submit' => array(
'title' => $this->l('Save'),
),
'buttons' => array(
array(
'href' => AdminController::$currentIndex.'&configure='.$this->name.'&token='.Tools::getAdminTokenLite('AdminModules'),
'title' => $this->l('Back to list'),
'icon' => 'process-icon-back'
)
)
);
I suppose the toolbar behaviour and purpose has changed along with the new backend theme.