title: Facebook API's method: isSessionValid() always returns true
body: <p>I am using the <a href="http://developers.facebook.com/docs/mobile/android/build/" rel="nofollow">official facebook SDK for Android</a> and I am facing some issues regarding session management. Specifically, I don't know how to test whether the session is still valid or not. </p>
  
  <p>First I initialize and authorize a connexion to facebook:</p>
  
  <pre><code>Facebook facebook = new Facebook(context.getString(R.string.facebook_app_id));
  facebook.authorize(...); // Works ok
  </code></pre>
  
  <p>Then, I want to disconnect the user:</p>
  
  <pre><code>facebook.logout(context);
  </code></pre>
  
  <p>But once I have done that, the following <strong>still</strong> returns <em>true</em>:</p>
  
  <pre><code>facebook.isSessionValid();
  </code></pre>
  
  <p>Why does it return <em>true</em>? </p>
  
  <p>Anything I'm doing wrong?</p>
  
  <p>Thanks!</p>