Plack does not come back from Catalyst

Question

I have an app that may choose to serve a file from disk - or go to Catalyst and generate a dynamic one.

Something like this (inside call()):

    if (-f $path){
        my $app = Plack::App::File->new(file => $path)->to_app; #serve published page
        $res = $app->($env);
    }else{
        log_debug  "Fall through to app ";
        $res = $self->app->($env);.
    }

I'd like to set some cookies when it gets back. So I use Plack::Util

   Plack::Util::response_cb($res, sub {
        my $res = shift;
        log_debug "Handling app response";
        ...
   });

The results? In the first case (Plack::App::File), everything works as expected. In the second (continue to the app the normal way) it never comes back in.

I wonder why this is happenning? Here is my psgi initialization:

my $app = MainApp->psgi_app(@_);
$app = Plack::MyAppAbove->wrap($app);  
$app = MainApp->apply_default_middlewares($app);