Shared context / global config before hooks called in wrong order

one_spec.rb

require_relative 'spec_helper'

describe 'A' do
  describe 'B', :a => :b do
    it 'succeeds' do
      puts 'succeeds'
    end
  end
end

shared_context.rb

shared_context 'shared_context', :a => :b do
  before(:all) do
    @global_variable.should be
  end  
end

spec_helper.rb

require 'rspec'
require_relative 'shared_context'

RSpec.configure do |config|
  config.before(:all) do
    @global_variable = 'string'
  end
end

two_spec.rb

require_relative 'spec_helper'

describe 'A', :a => :b do
  it 'fails' do
    puts 'fails'
  end
end