Associations in Rails 4 return a CollectionProxy instead of an Array

article.rb

class Article < ActiveRecord::Base
  has_and_belongs_to_many :tags
end

articles_controller.rb

class ArticlesController < ApplicationController
  respond_to :json, :html

  def show
    respond_with @article = Article.find(params[:id])
  end
end

tag.rb

class Tag < ActiveRecord::Base
  has_and_belongs_to_many :articles
end

tags_controller.rb

class TagsController < ApplicationController
  respond_to :json, :html

  def index
    @tags = Tag.all
  end
end