Respond with :json — strange behavior

Rails
1

I have a controller:

class ItemsController < ApplicationController
respond_to :json

def index
  groups = Item.all

  respond_with(items)
end

end

I am curling my_app/items.json and see a response with JSON object
just
as expected. At this point I don’t have any views associated with
controller, specifically I don’t have index.html.erb (.html).

Now if only I create an index.haml (for instance), with a simple %h1
Hello, world! line, requesting (again via curl) my_app/items.json
returns
an html string with

Hello, world!

. Note that I didn’t alter
the
controller code it just remains untouched.

I’m sure I’m missing something. Any help on explaining of what’s
happening
here?

2

Oh, it’s Rails 3.2.0.rc1 by the way.