Why are JS requests using layouts?

Ben Johnson wrote:

If I specify a layout in a controller:

class MyController < ApplicationController
layout "some_layout"

Any JS request will use the some_layout. I thought certain requests
types were exempt from layouts? When I remove the layout call everything
works perfect, the problem is that it uses the application layout.

Any ideas why this is or how I can fix this?

Is this with a recent version of Rails?
At one time you had to do

layout proc {|controller| 'some_layout' unless controller.request.xhr?}

But if you're doing proper RJS renders, I don't think it's now necessary.