Is Laravel 5.1 App:singleton not working properly?

Given this code, placed in the default file routes.php in Laravel 5.1:

    App::singleton('CatalogsService', function(){
            return new CatalogsService;
        });   

Route::group(['prefix' => 'catalogs'], function() {
    Route::get('statesmx', function (){       

        return var_dump(app('CatalogsService'));
    });

    Route::get('statesmx2', function() {
        return var_dump(app('CatalogsService'));
    });

    Route::get('statesmx3', function() {
        return var_dump(app('CatalogsService'));
    });

});

Why am I getting a different instance of CatalogsService when navigating to the 3 defined routes?

localhost/catalogs/statesmx dumps:

object(AppServicesCommonCatalogsService)[152]

localhost/catalogs/statesmx2 dumps:

object(AppServicesCommonCatalogsService)[153]

localhost/catalogs/statesmx3 dumps:

object(AppServicesCommonCatalogsService)[154]

I was expecting to get the same Object Reference Id.

The only way to get the same reference is by adding the next code before the Route::group....

app('CatalogsService');

when I do it the 3 routes dump the same object reference:

object(AppServicesCommonCatalogsService)[106]

I don't get it why is this happening. For me it looks Laravel Singleton is not working properly unless there's something I'm missing about the way a Singleton in Laravel works.

Thank you in advance for any help or hint on this matter.

PD: I'm new to Laravel.