dm-redis-adaptor has n, :through associations incomplete after reload

gistfile1.rb

class User
  include DataMapper::Resource
  property :id, Serial
  property :full_name,            String,   :length => 25, :required => true
  property :email,                String,   :length => 320, :required => true

  has n, :company_memberships
  has n, :companies, :through => :company_memberships
end

class Company
  include DataMapper::Resource
  property :id,           Serial
  property :name,         String, :required => true

  has n, :company_memberships
  has n, :users, :through => :company_memberships
end


class CompanyMembership
  include DataMapper::Resource

  belongs_to :user, :key => true
  belongs_to :company, :key => true
end

# I call flushall on Redis before performing the following:

u = User.create :full_name => 'Joe Blow', :email => 'joe@example.com'
c = Company.create :name => 'Sprockets'

u.companies << c
u.save
#=> true

u.companies
#=> [#<Company @id=1 @name="Sprockets">]
u.company_memberships
#=> [#<CompanyMembership @user_id=1 @company_id=1>]

u1 = User.first
u1 == u
#=> true

u1.companies
#=> [#<Company @id=1 @name="Sprockets">]
u1.company_memberships
#=> []

c1 = Company.first
c1 == c
#=> true

c1.users
#=> [#<User @id=1 @username="JoeBlow" @full_name="Joe Blow" @email="joe@example.com">]
c1.company_memberships
#=> []

CompanyMembership.all
#=> [#<CompanyMembership @id=nil @user_id=nil @company_id=nil>]