Form validation: Is "htmlspecialchars" run no matter what?

[eluser]davidbehler[/eluser]
Ok, I have this setup:

form_validation.php in config folder:

Code:

$config = array
   (
      'post' => array
                  (
                     array
                        (
                           'field' => 'post_content',
                           'label' => 'Content',
                           'rules' => 'trim|required|xss_clean'
                        )
                  )
   )

test.php in controller folder:

Code:

function post()
   {
      $this->load->library('form_validation');
      if ($this->form_validation->run('post') == FALSE)
      {
         // show error message
      }
      else
      {
         // do some stuff
      }
      $this->load->view('post');
   }

post.php in view folder:

Code:

echo form_open('test/post');

$data = array(
            'name' => 'post_content',
            'id' => 'post_content',
            'cols' => '100',
            'rows' => '5',
            'value' => set_value('post_content')
);

echo form_textarea($data);


echo form_submit(array('value'=>'submit'));
echo form_close();

So far so easy, but now I got the following problem:
No matter what I enter into textarea, it seems like it's run through "htmlspecialchars", even though I have no such rule defined!

Example:
Entered value: <p>test</p>
"echo set_value('post_content');" BEFORE the validation is run: &lt;p&gt;test&lt;/p&gt;
"echo set_value('post_content');" AFTER the validation is run: ltpgt;testlt;/pgt; (damn board keeps escaping my examples..)

Anyway, the first echo returns the value just like I entered it, the second one returns it as run through "htmlspecialchars" even though there is no such rule for that field!

Any ideas why?
Help appreciated!