How does "respond_with_navigational" work?

I'm working with Devise and DeviseInvitable to manage authentication in my app and I'm having some trouble adding AJAX support to InvitationsController#update. The controller in DeviseInvitable looks like this:

# invitations_controller.rb

# PUT /resource/invitation                                                                                                 
def update
  self.resource = resource_class.accept_invitation!(params[resource_name])

  if resource.errors.empty?
    set_flash_message :notice, :updated
    sign_in(resource_name, resource)
    respond_with resource, :location => after_accept_path_for(resource)
  else
    respond_with_navigational(resource){ render_with_scope :edit }
  end
end

This works well when resource.errors.empty? == true and we execute:

respond_with resource, :location => after_accept_path_for(resource)

(i.e. invitations/update.js.erb is rendered and my javascript calls are made). The problem is that when resource.errors.empty? == false, and we execute:

respond_with_navigational(resource){ render_with_scope :edit }

the server says:

Rendered invitations/update.js.erb (1.4ms)

but my javascript calls are not being run. Can anyone explain what respond_with_navigational is supposed to be doing? I've been googling for hours and I haven't found an explanation of this api anywhere.

Thanks!