Issue deleting items with filter search - cakephp

Question

I am developing a plugin for CakePHP 2.
My problem is below:
I have a view with a filter search, where users can search by category:
<div>
<?php echo $this->Form->create('Permission'); ?>
<fieldset>
<?php echo $this->Form->input("permissionCategory", array('label' =>
__d('permission_manager','Categoría'), 'options' => $categorias, 'empty' =>
__d('permission_manager','-- Categorías --'), 'default' => '','class' => 'select-cat', 'onchange' => 'this.form.submit()')); ?>
</fieldset>
<?php //echo $this->Form->end(__d('permission_manager','Aceptar')); ?>
</div>
When I do click over delete button, it shows the confirm message, but when I push yes, the item is not deleted.
I realized it has relation with the action. Maybe with the request type.
The action code:
public function index() {
$this->paginate = array('order' => 'Permission.category asc, Permission.code asc');
$this->Permission->recursive = 2;
if($this->request->is('post')) {
if(empty($this->request->data['Permission']['permissionCategory'])) {
$conditions = null;
} else {
$cat = $this->Permission->findById($this->request->data['Permission']
['permissionCategory']);
$conditions = array('Permission.category ' => $cat['Permission']['category']);
}
$this->Paginator->settings = array(
'conditions' => $conditions );
}
$this->set('categorias', $this->Permission->find('list', array('fields' => 'category',
'group' => 'category')));
$this->set('permissions', $this->Paginator->paginate());
}
Edit:
My delete button:
(I have one like this for row in DB)
<?php echo $this->Form->postLink($this->Html->image('PermissionManager.cross.png',
array('title' =>
__d('permission_manager','Borrar'))),'delete/'.h($permission['Permission']['id']),
array( 'escape' => false), __d('permission_manager','Are you sure... ?'));
?>
My delete action:
public function delete($id = null) {
$this->Permission->id = $id;
if (!$this->Permission->exists()) {
//throw new NotFoundException(__d('permission_manager','Permiso inexistente'));
$this->Session->setFlash(__d('permission_manager','Permiso inexistente'), 'default', array('class'=>'error'));
return $this->redirect(array('action' => 'index'));
}
$this->request->onlyAllow('post', 'delete');
if ($this->Permission->delete()) {
$this->Session->setFlash(__d('permission_manager','El permiso ha sido borrado correctamente.'), 'default', array('class'=>'success'));
} else {
$this->Session->setFlash(__d('permission_manager','El permiso no ha podido borrarse. Por favor, inténtelo de nuevo.'), 'default', array('class'=>'error'));
}
return $this->redirect(array('action' => 'index'));
}