title: onSaveInstanceState not called on Fragment
body: <p>I am replacing a Fragment with another one:</p>
  
  <pre><code>    FragmentTransaction transaction = mFragmentManager.beginTransaction();
  
      transaction.setCustomAnimations(R.anim.enter, R.anim.exit, R.anim.pop_enter, R.anim.pop_exit);
      transaction.replace(R.id.main_container, nextFragment, nextFragment.getClass().toString());
      transaction.addToBackStack(nextFragment.getClass().toString());
      transaction.commit();
  </code></pre>
  
  <p>however, the fragment thats being replaced, its onSaveInstanceState is not called. what am i doing wrong?</p>