DataMapper collection bug

gistfile1.rb

require 'rubygems'

dm_version = "=1.2.0"
gem     "dm-core",        dm_version
require 'dm-core'

gem     "dm-migrations",  dm_version
require 'dm-migrations'

class Thing
  include DataMapper::Resource
  
  property    :id,             Serial,   :key => true
  
  has n,      :tags
end

class Tag
  include DataMapper::Resource
  
  property    :id,             Serial, :key => true
  
  belongs_to :thing
end

DataMapper.finalize
DataMapper.setup(:default, "sqlite3://#{Dir.pwd}/test.sqlite3")

DataMapper.auto_migrate!
    
thing = Thing.create
    
thing.tags.create

tag = thing.tags.first

if thing.tags.size == 1
  puts "OK"
else 
  raise "Expected 1 tag got #{thing.tags.size}"
end