Rails 5 routing issue with prefixed optionals

test_425.rb

begin
  require 'bundler/inline'
rescue LoadError => e
  $stderr.puts 'Bundler version 1.10 or later is required. Please update your Bundler'
  raise e
end

gemfile(true) do
  source 'https://rubygems.org'
  # Activate the gem you are reporting the issue against.
  gem 'rails', '4.2.5'
end

require 'rack/test'
require 'action_controller/railtie'

class TestApp < Rails::Application
  config.root = File.dirname(__FILE__)
  config.session_store :cookie_store, key: 'cookie_store_key'
  secrets.secret_token    = 'secret_token'
  secrets.secret_key_base = 'secret_key_base'

  config.logger = Logger.new($stdout)
  Rails.logger  = config.logger

  routes.draw do
    get 'prefixed_optional(/p-:page)', to: 'test#prefixed_optional', as: :prefixed_optional
  end
end

class TestController < ActionController::Base
  include Rails.application.routes.url_helpers

  def prefixed_optional
    render plain: 'Home'
  end
end

require 'minitest/autorun'

# Ensure backward compatibility with Minitest 4
Minitest::Test = MiniTest::Unit::TestCase unless defined?(Minitest::Test)

class BugTest < Minitest::Test
  include Rack::Test::Methods

  def test_returns_success
    get '/prefixed_optional/p-12'
    assert last_response.ok?
  end

  private
    def app
      Rails.application
    end
end

test_master.rb

begin
  require 'bundler/inline'
rescue LoadError => e
  $stderr.puts 'Bundler version 1.10 or later is required. Please update your Bundler'
  raise e
end

gemfile(true) do
  source 'https://rubygems.org'
  gem 'rails', github: 'rails/rails'
  gem 'arel', github: 'rails/arel'
  gem 'rack', github: 'rack/rack'
  gem 'sprockets', github: 'rails/sprockets'
  gem 'sprockets-rails', github: 'rails/sprockets-rails'
  gem 'sass-rails', github: 'rails/sass-rails'
end

require 'action_controller/railtie'

class TestApp < Rails::Application
  config.root = File.dirname(__FILE__)
  config.session_store :cookie_store, key: 'cookie_store_key'
  secrets.secret_token    = 'secret_token'
  secrets.secret_key_base = 'secret_key_base'

  config.logger = Logger.new($stdout)
  Rails.logger  = config.logger

  routes.draw do
    get 'prefixed_optional(/p-:page)', to: 'test#prefixed_optional', as: :prefixed_optional
  end
end

class TestController < ActionController::Base
  include Rails.application.routes.url_helpers

  def prefixed_optional
    render plain: 'Home'
  end
end

require 'minitest/autorun'
require 'rack/test'

class BugTest < Minitest::Test
  include Rack::Test::Methods

  def test_returns_success
    get '/prefixed_optional/p-12'
    assert last_response.ok?
  end

  private
    def app
      Rails.application
    end
end