render_to_string :partial sets response.content_type

Tested on Edge Rails:

The following controller code produces a different content type header on Rails 2.1 and 2.2:

class TestController < ApplicationController
  def index
    render(:json => {:content => render_to_string(:partial => 'test') } )
  end
end

Expected Content Type: application/json

Rails 2.1 Content Type: application/json

Rails 2.2 Content Type: text/html

In Rails 2.1 response.content_type is still nil after render_to_string. In 2.2 render_to_string :partial changes response.content_type to text/html. Because of this the render :json call will not set the content_type correctly.