title: Facebook logout does not work Android [Facebook sdk 4]
body: <p><br/>
  I'm developing a game for Android that has Facebook login and I faced the following weird behaviour when trying to logout:<br/>
  if user press Facebook logout button, closes the app and then reopens again, the user is still logged in (= access token still valid).
  As a test, I checked the access token after logout and it is null as it should be, but if I close and reopen the app then the access token is again not null.<br/>
  It seems that Facebook caches the access token and takes it from cache even after logout.
  <br/><br/>
  I tried using native Facebook button and also LoginManager.getInstance.logout(); I have initialized Facebook sdk on the top of the onCreate, before setContent() and I followed the procedure on Facebook docs, but same result.
  <br/><br/>
  I'm using Facebook sdk 4.6.0 and I faced this problem on Android 4.2.2 and 4.4.2.
  <br/><br/>
  <strong>EDIT</strong><br/><br/>
  Here's the code:<br/><br/>
  - Facebook button:<br/><br/></p>
  
  <pre><code>@Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      FacebookSdk.sdkInitialize(getApplicationContext());
      setContentView(R.layout.activity_settings);
      btnFacebookLogout.registerCallback(callbackManager, new FacebookCallback&lt;LoginResult&gt;() {
          @Override
          public void onSuccess(LoginResult loginResult) {
  
          }
  
          @Override
          public void onCancel() {
          }
  
          @Override
          public void onError(FacebookException e) {
  
          }
      });
  }
  </code></pre>
  
  <p><br/><br/>
  - normal button:<br/><br/></p>
  
  <pre><code>btnNormalLogout.setOnClickListener(new View.OnClickListener() {
          @Override
          public void onClick(View v) {
              LoginManager.getInstance().logOut();
          }
      });
  </code></pre>
  
  <p>Any suggestion?
  <br/><br/>
  Thanks in advance</p>