проблема has_many_polymorphs

у меня есть проблема с has_many_polymorphs, возможно, можно помочь мне.

У меня есть некоторые модели

class Issue < ActiveRecord::Base
  has_many_polymorphs :things, :from => [:applications], :through => :relations
ene

class NewsArticle < ActiveRecord::Base
  has_many_polymorphs :things, :from => [:applications], :through => :relations
end

class Application < ActiveRecord::Base
  has_many_polymorphs :contents, :from => [:news_articles, :issues], :through => :relations
end  

class Relation < ActiveRecord::Base
  belongs_to :content, :polymorphic => true
  belongs_to :thing, :polymorphic => true

  acts_as_double_polymorphic_join(
   :contents => [:news_articles, :issues],
   :things => [:applications]
  )
end

но на попытке получить приложения для некоторой проблемы я вижу следующее

>> i = Issue.first
+----+--------+---------+----------+---------------+----------------+-------------+-------------+-----------------+---------------------------+---------------------------+
| id | closed | user_id | answered | answers_count | comments_count | views_count | flags_count | favorites_count | created_at                | updated_at                |
+----+--------+---------+----------+---------------+----------------+-------------+-------------+-----------------+---------------------------+---------------------------+
| 1  | false  | 2       |          | 2             | 2              | 0           | 0           | 0               | 2010-04-22 00:14:56 +0400 | 2010-05-01 02:35:30 +0400 |
+----+--------+---------+----------+---------------+----------------+-------------+-------------+-----------------+---------------------------+---------------------------+
1 row in set
>> i.applications
ActiveRecord::HasManyThroughSourceAssociationNotFoundError: Could not find the source association(s) :application in model Relation.  Try 'has_many :applications, :through => :relation, :source => <name>'.  Is it one of :content or :thing?
        from /opt/local/lib/ruby/gems/1.8/gems/activerecord-2.3.5/lib/active_record/reflection.rb:289:in `check_validity!'
        from /opt/local/lib/ruby/gems/1.8/gems/activerecord-2.3.5/lib/active_record/associations/has_many_through_association.rb:5:in `initialize'
        from /opt/local/lib/ruby/gems/1.8/gems/activerecord-2.3.5/lib/active_record/associations.rb:1300:in `new'
        from /opt/local/lib/ruby/gems/1.8/gems/activerecord-2.3.5/lib/active_record/associations.rb:1300:in `applications'
        from (irb):2
        from :0
>> 

в журналах я вижу

** has_many_polymorphs: autoload hook invoked
** has_many_polymorphs: preloading parent model Application
** has_many_polymorphs: preloading parent model Issue
** has_many_polymorphs: preloading parent model NewsArticle
** has_many_polymorphs: preloading parent model Relation
** has_many_polymorphs: autoload hook invoked
** has_many_polymorphs: preloading parent model Application
** has_many_polymorphs: preloading parent model Issue
** has_many_polymorphs: preloading parent model NewsArticle
** has_many_polymorphs: preloading parent model Relation
  Issue Load (0.9ms)   SELECT * FROM "issues" LIMIT 1

Как решить его?

PS: направляющие 2.3.5, Postgresql