CodeIgniter doesn't load default controller on '/' - php

Question

I'm using CodeIgniter with Nginx.
I have just upgraded from CodeIgniter 2.2.6 to 3.1.4, following all the changelogs and upgrade instruction. Everything works perfectly but the default controller, i.e. http://francescoruvolo.it (or even http://francescoruvolo.it/index.php) shows a 404 page but all other routing rules works and I'm able to load the other controllers.
Here is my routes.php:
$route['(it|en)/contact/check_form'] = "Email/validate_form/$1";
$route['(it|en)/contact'] = "Email/show_form/$1";
$route['(it|en)/(:any)'] = "Pages/show/$1/$2";
$route['(it|en)'] = "Pages/show/$1";
$route['default_controller'] = "Pages/show/";
$route['404_override'] = '';
$route['translate_uri_dashes'] = FALSE;
I have also tried to comment all routes, but still the default one is ignored. Still, if I go http://francescoruvolo.it/Pages/show or either http://francescoruvolo.it/en, controllers are loaded just fine and it works. Many people had similar problems because they missed the part about enforcing the capitalized name for classes, but this is not the case as my controllers' name have been already fixed.
These are the parameters in config.php:
$config['base_url'] = 'http://francescoruvolo.it/';
$config['index_page'] = '';
$config['uri_protocol'] = 'REQUEST_URI';
And Nginx looks like it is properly forwarding all requests to index.php, in fact I don't need to specify it when loading controllers explicitly. Anyway, these lines are part of my Nginx configuration for the host:
location / {
try_files $uri $uri/ /index.php;
}
What I don't get is that I'm actually able to get two different kind of 404 pages. For example, if I go to http://francescoruvolo.it/nonexistent.php Nginx correctly serves me a 404 page. At the same time, if I do not specify any path or explicitly specify index.php I get a 404 "well formatted", which means that the index.php from CodeIgniter has been actually run, but it failed to load the controller.
What am I missing? What else can I check?

Answer 1

Solved. Apparently, I had an extra (unneeded) / at the end of my default route.
This was WRONG:
$route['default_controller'] = "Pages/show/";
This is CORRECT:
$route['default_controller'] = "Pages/show";
Still, I don't quite get why. In fact, if I explicitly load the controller, it works even with the extra slash.
If anyone explains this, I'll gladly accept his answer. :)