Interferes with Capybara tests even when only added to dev group

Hey there -- it doesn't seem that this issue has been raised yet, and I don't even know if this issue is necessarily the fault of this gem, but I'm opening this in the hopes that I can get some pointers.

It seems that adding better_errors is interfering with Capybara feature tests, even when it's added only to the development group.

Here's what I did:
- Made a simple vanilla Rails app (4.2.1)
- Added rspec-rails (3.2.1)
- Ran `rails g rspec:install`
- Added the following to config/routes.rb: `get /users, to: "users#index"`
- Added the following test to spec/features/my_feature_spec.rb

``` ruby
require 'rails_helper'

feature 'My feature' do
scenario 'is awesome' do
visit '/users'
expect(page).to have_content('Users')
end
end
```
- Ran the test. As expected, it fails with: `ActionController::RoutingError: uninitialized constant UsersController`
- Then, I added better_errors to the Gemfile, but only in the development group
- Ran the test again. Now it passes! How? Well, if you throw in a `save_and_open_page` then you'll get the text version of better_errors:

``````
ActionController::RoutingError at /users
========================================

> uninitialized constant UsersController

spec/features/my_feature_spec.rb, line 5
----------------------------------------

``` ruby
1 require 'rails_helper'
2
3 feature 'My feature' do
4 scenario 'is awesome' do
> 5 visit '/users'
6 expect(page).to have_content('Users')
7 save_and_open_page
8 end
9 end

... etc., etc. ...
``````

I realize this may be "expected" behavior, but my question is, why is this happening?