php - cakephp edit action and requests?

So can someone explain this to me? I'm trying to write an edit action and am a bit unsure of why the following does not work:

public function edit($id = null) {

    if (!$id) {
        throw new NotFoundException('NO ID HAS BEEN SUPPLIED');
    } 

    $data = $this->User->findById($id); 

    if(!$this->request->is('post')) { $this->request->data = $data;   }


    if($this->request->is('post') || $this->request->is('put')) { 
       $this->User->id = $id; 
       $this->User->save($this->request->data);
       $this->redirect(array('action'=>'index'));
   } 
}
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And by not working, I mean, that while it does pre-populate the form with data gathered from findById($id).. it doesn't update the database with the new inputs after the form has been sent.

I have replaced this:

if(!$this->request->is('post'))
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With the following:

if($this->request->is('get'))
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And suddenly, it works fine. It updates the row with the new values gathered from the post. However, I do not understand what's happening here. Why is it that !$this->request->is('post), does NOT work, while $this->request->is('get') DOES work? Surely, when the action is first called it is called using a GET request? Doesn't that request qualify as !$this->request->is('post')?

EDIT:

below is the ctp: app/View/Users/edit.ctp

 <?php echo $this->Form->create('User'); ?>

     <fieldset>
    <legend><?php echo __('edit User'); ?></legend>

    <?php 
    echo $this->Form->input('username');
    echo $this->Form->input('password');
    echo $this->Form->input('role');
   // echo $this->Form->input('role', array(
     //   'options' => array('admin' => 'Admin', 'regular' => 'Regular')
    //));//
?>
</fieldset> <?php echo $this->Form->end(__('Submit')); ?>
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