set_value() not working on custom validation field

[eluser]ci_user[/eluser]
set_value() not working on custom validation field. The posted value for the custom validation field comes back empty on page reload when validation fails.

The view:

Code:

$date = array(
'name' => 'date',
'value' => set_value('date'),
'id' => 'datepicker'
);
&lt;?=form_error('date');?&gt;<label>Date: </label>&lt;?=form_input($date);?&gt;

The controller:

Code:

$this->form_validation->set_rules('date', 'Date', 'trim|required|valid_date');
$this->form_validation->set_message('valid_date', 'The date format must be dd/mm/yyyy.');

My_Form_Validation:

Code:

public function valid_date($val)
    {
        if(!preg_match('^(0[1-9]|1[012])[/](0[1-9]|[12][0-9]|3[01])[/](19|20)\d\d$^', $val)){
return false;
     }
}