format.atom renders builder templates inside HTML application layout in 2.3.0

Given a builder template at "app/views/posts/index.atom.builder", in
2.2.2 my controller methods could render atom feeds like this:

  format.atom { @posts = Post.find(:all) }

As of 2.3.0 RC1, that code produces unusable feeds because they get
rendered _inside_ the application layout (HTML). So I now need to
render like this:

  format.atom {
    @posts = Post.find(:all)
    render :layout => false
  }

Is this a bug/regression in 2.3.0 RC1? Or was I just lucky in the past
because the old behaviour was not intended?

And if the new behaviour _is_ intended, is there a way I can set a
default layout (false) for the atom format in one single place,
instead of having to do it explicitly in every action of every
controller?

Cheers,
Wincent

And if the new behaviour _is_ intended, is there a way I can set a
default layout (false) for the atom format in one single place,
instead of having to do it explicitly in every action of every
controller?

The workaround I'm currently testing is sticking this in my
application_controller.rb:

  layout Proc.new { |controller| controller.send(:is_atom?) ? false :
'application' }

Where "is_atom?" is just this method:

  def is_atom?
    params[:format] == 'atom'
  end

Still wondering though, why this used to work pre-2.3.0 and what/why
it has has changed all of a sudden...

Is this a bug/regression in 2.3.0 RC1? Or was I just lucky in the past
because the old behaviour was not intended?

Cheers,
Wincent