title: CakePHP saveAll/saveAssociated issue
body: <p>I'm a bit confused with the following CakePHP outcome. I included code for two Model and one Controller (stripped out unnecessary stuff).</p>
  
  <p><strong>Problem: Everything saves correctly. The only issue is the user_id field for the store_users table does not save.</strong></p>
  
  <p>Anything obvious you can see that I'm doing wrong? I tried with both saveAssociated and saveAll.</p>
  
  <p><strong>Model/Store.php</strong></p>
  
  <pre><code>&lt;?php
  App::uses('AppModel', 'Model');
  class Store extends AppModel {
      public $belongsTo = array(
          'User'
      );
      public $hasMany = array(
          'StoreUser'
      );
  }
  </code></pre>
  
  <p><strong>Model/StoreUser.php</strong></p>
  
  <pre><code>&lt;?php
  App::uses('AppModel', 'Model');
  class StoreUser extends AppModel {
      public $belongsTo = array(
          'User',
          'Store'
      );
  }
  </code></pre>
  
  <p><strong>Controller/StoresController.php</strong></p>
  
  <pre><code>&lt;?php
  App::uses('AppController', 'Controller');
  class StoresController extends AppController {
      public $uses = array('Store');
  
      public function create() {
          $this-&gt;Store-&gt;create();
          $storeData = array(
              'Store' =&gt; array(
                  'title' =&gt; 'New Store',
                  'user_id' =&gt; $this-&gt;Auth-&gt;user('id')
               ),
               'StoreUser' =&gt; array(
                   'user_id' =&gt; $this-&gt;Auth-&gt;user('id')
                )
          );
          if($this-&gt;Store-&gt;saveAll($storeData) !== false) {
              // Success
          } else {
              // Error
          }
      }
  }
  </code></pre>
  
  <p><strong>Results in DB</strong></p>
  
  <pre><code>stores table:
      id: 1
      title: New Store
      user_id: 1
      ...
  
  store_users table:
      id: 1
      store_id: 1
      user_id: 0
      ...
  </code></pre>