Rspec + Capybara: controller missing, integration spec passes anyway - ruby-on-rails

Question

I started a fresh new rails app (using rspec-rails 2.99 & capybara 2.3.0), and wrote a silly simple integration spec to get started with TDD:
# spec/integration/visit_home_page_spec.rb
require 'spec_helper'
feature "view the home page" do
scenario "user visits home page" do
visit root_path
expect(page).to have_content 'Password'
end
end
As expected, the test fails due to root_path being undefined - so I went ahead and:
# config/routes.rb
root 'users#new'
And here's the problem: instead of the spec failing due to UsersController being undefined, it's green. It appears that rspec is evaluating the error page itself, and since that page happens to contain the word "password", the spec passes.
To make sure that's what's happening, I have modified the spec to:
# spec/integration/visit_home_page_spec.rb
...
expect(page).to have_content 'theresnowaythisisinthepage'
...
Now the test fails, but not because it's picking up the undefined UsersController - just because the content is not in the error page.
I've started many an app with this approach, and it's the first time I've seen rspec mistaking an error page for a valid one - what did I break?
I suspect my forehead will have a big hand-shaped mark when I find the answer.
--
Here's my Gemfile
source 'https://rubygems.org'
gem 'rails', '~> 4.1.1'
gem 'mysql2', '~> 0.3.16'
gem 'sass-rails', '~> 4.0.2'
gem 'uglifier', '>= 1.3.0'
gem 'coffee-rails', '~> 4.0.0'
gem 'jquery-rails'
gem 'active_model_serializers', '~> 0.8.1'
gem 'slim-rails', '~> 2.1.4'
gem 'bootstrap-sass', '~> 3.1.1.1'
gem 'bootstrap-generators', '~> 3.1.1.3'
group :test, :development do
gem 'rspec-rails', '~> 2.99'
gem 'capybara', '~> 2.3.0'
end
group :development do
gem "better_errors"
gem "binding_of_caller" # required by better-errors
gem "launchy"
end
group :doc do
gem 'sdoc', require: false
end
Here's spec_helper
require File.expand_path("../../config/environment", __FILE__)
require 'rspec/rails'
Dir[Rails.root.join("spec/support/**/*.rb")].each { |f| require f }
ActiveRecord::Migration.maintain_test_schema!
RSpec.configure do |config|
config.fixture_path = "#{::Rails.root}/spec/fixtures"
config.use_transactional_fixtures = true
config.infer_base_class_for_anonymous_controllers = false
config.order = "random"
config.infer_spec_type_from_file_location!
config.include Capybara::DSL
end