Undefined Index for … existing index?

OK, that's more than weird...

Here's my code :

public function results($id,$pattern=3)
{
    $this->load->library('session');

    if (!$this->session->userdata('logged_in'))
    {
        $this->session->set_flashdata('return_url',$this->uri->uri_string());
        redirect('log/in','refresh');
    }
    else
    {
        $this->load->model('projects');

        $proj = (array)$this->projects->getProjectById($id);

        print_r($proj);

        $progressPercentage = number_format((float)( ($proj['progress'] * 100) / $proj['total'] ), 2, '.', '');

    }
}

Now, here's the issue :

When NO $pattern is passed to the controller, the whole thing works fine.

When I pass some parameter, like mysite.com/project/results/45/4 (pattern=4), I'm getting the following error :

A PHP Error was encountered

Severity: Notice

Message: Undefined index: progress

Filename: controllers/project.php

Line Number: 75

The weird thing is that both $id and $pattern are "read" fine.

When I'm print_ring $proj just before the line concerning undefined index this the results I'm getting :

Array ( [id] => 21240 [email] => my@gmail.com [url] => somewebsite.com [domains] => another_domain [progress] => 198 [total] => 199 [alias] => Test Project #3 [status] => complete )

And well as you can obviously see for yourself, the progress index is perfectly there.

So, what could the issue be? Is that any weird know CI bug?

This is what var_dump($proj,$proj['progress']); gives :

array(8) {
  ["id"]=>
  string(5) "21240"
  ["email"]=>
  string(20) "my@gmail.com"
  ["url"]=>
  string(27) "somewebsite.com"
  ["domains"]=>
  string(84) "another_domain"
  ["progress"]=>
  string(3) "198"
  ["total"]=>
  string(3) "199"
  ["alias"]=>
  string(15) "Test Project #3"
  ["status"]=>
  string(8) "complete"
}
string(3) "198"

It should be like: