Why is my options menu not showing the settings menu item correctly?

Question

I This is from https://developers.facebook.com/docs/android/scrumptious/authenticate

This is my code (identical from the tutorial) for the options menu part

@Override
    public boolean onPrepareOptionsMenu(Menu menu) {
        // only add the menu when the selection fragment is showing
        if (fragments[SELECTION].isVisible()) {
            if (menu.size() == 0) {
                settings = menu.add(R.string.settings);
            }
            return true;
        } else {
            menu.clear();
            settings = null;
        }
        return false;
    }
    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        if (item.equals(settings)) {
            showFragment(SETTINGS, true);
            return true;
        }
        return false;
    }

whats happening is this works most of the time but I found a test case I couldn't debug. When you logout, the menu item still shows and you have to click it to make it disappear.(it shouldn't appear at all). This wasn't a huge concern to me at the beginning but I found that when you logged in again after you clicked the menu item to make it disappear, the options menu doesn't appear at all.

Answer 1

I think I found the problem, I leave it up for others. From When and how often onPrepareOptionsMenu() method is called for ActionBar? ,I got that "On Android 3.0 and higher, you must call invalidateOptionsMenu() when you want to update the menu, because the menu is always open. The system will then call onPrepareOptionsMenu() so you can update the menu items." When I logged out, even thought there were no actual menu items, the menu was still open. However when I clicked the menu when it was empty, it messed it up so that when I logged in, show wouldn't work. I don't understand that part yet. I was hoping someone can elaborate what happened during that part