Callbacks and array ?

[eluser]quasiperfect[/eluser]
i use the latest https://github.com/EllisLab/CodeIgniter
i have in the controller

Code:

$this->load->library('form_validation');  $this->form_validation->set_rules('myarray[]', 'myarray', 'callback__myarray_check');
if ($this->form_validation->run() == FALSE)
{
}
else
{
}
$this->load->view('welcome_message');

the callback function is

Code:

function _myarray_check($str) {
print_r($str);
echo '|';
$this->form_validation->set_message('_myarray_check', 'myarrayerror');
return FALSE;
}

in the view

Code:

<form method="post" action="welcome/">
<input type="checkbox"  name="myarray[]" value="1"> a, <input type="checkbox" name="myarray[]" value="2"> b
<?php echo (form_error('myarray[]'))?(form_error('myarray[]')):('');?>
<input type="submit" value="test">
</form>

on submit i get 1|2|
so the callback is called for each value of the array
is this intended ?
is a bug ?
to me more logical would be to get the array as parameter and to execute the callback once

edit
if nothing is selected the callback is not even called