title: Doctrine update issue in Symfony2
body: <p>I wrote some classes and generate related tables onto DB with <code>php app/console doctrine:generate:entities</code> <br/>
  Suddenly I understand that I've done something wrong and I've changed something into that classes: Have three classes (A,B,C) where A was connected to B and C is stand alone (for now)) but my schema have to connect A to C. So I modify all classes in a consistent manner and launched <code>php app/console doctrine:schema:update --force</code>.</p>
  
  <p>With big surprise, I notice that onto DB no changes were happened!<br/>
  How could this be possible? Have doctrine a file that he cached something or similar?</p>
  
  <p>P.S.: Relationships between entities are many-to-many</p>