Codeigniter路由错误涉及下划线

I'm having a problem with Codeigniter routing which involves underscores in controller class names. Here's my problem and how to replicate it.

1) clone or download Codeigniter and save in a folder in htdocs called 'test'

git clone https://github.com/bcit-ci/CodeIgniter.git

2) create the following controller and save as C_track.php:

class C_track extends CI_Controller {
  public function index(){ echo "index done"; }
  public function demo(){ echo "demo done"; }
}

3) add the following route:

$route['track']= 'C_track';

4) Set 'base_url' within config.php correctly (for my setup, it's...):

$config['base_url'] = 'http://localhost:8888/test/';  

At this point, if I go to: http://localhost:8888/test/index.php/track/ I see: index done

but, if I go to: http://localhost:8888/test/index.php/track/demo I get a 404 error.

I am expecting to see: demo done

Ok, now things get strange

5)create the following controller and save as Track.php:

class Track extends CI_Controller {
  public function index(){ echo "index DONE!!!"; }
  public function demo(){ echo "demo DONE!!!"; }
}

6) Do not add a new route!

At this point, if I go to: http://localhost:8888/test/index.php/track/ I see: index done

but, if I go to: http://localhost:8888/test/index.php/track/demo I see: demo DONE!!!

This is not what I am expecting. For some reason, Codeigniter is running the demo function within Track.php, even though the file is not even listed in routes.php. I'm guessing that the underscore is the problem. because:

7) change routes.php:

$route['track']= 'Track';

Now, if I go to: http://localhost:8888/test/index.php/track/ I see: index DONE!!!

but, if I go to: http://localhost:8888/test/index.php/track/demo I see: demo DONE!!!

Which is exactly what I expect to see!!

How can I fix this? I would really like to find a way to solve this problem so that underscores work as expected, because my naming scheme is based heavily on underscores in file names & class names.