android fragment addToBackStack bug

In FragmentActivity。First, I add two fragment by FragmentTransaction。
See the flowing code :
/******************************************************/
MyFragmentManager manager;
FragmentTransaction fragmentTransaction;
FragmentManager fragmentManager;
MainBottomFragment bottom;
fragmentManager = getSupportFragmentManager();
fragmentTransaction = fragmentManager.beginTransaction();
manager = new MyFragmentManager(this);
Fragment bottomFragment =  new MainBottomFragment(this);
Fragment homePageFragment= new HomePageFragment(this);
fragmentTransaction.add(R.id.common_bottom, bottomFragment);
fragmentTransaction.add(R.id.common_top, homePageFragment= );
fragmentTransaction.commit();
/******************************************************/
Second,In homePageFragment fragment,I need to deal with one button click event to next fragment(A),
then in Fragment,I processing then:
/******************************************************/
getSupportFragmentManager().beginTransaction().addToBackStack(null).replace(R.id.common_top, A);
/******************************************************/
Third,In A fragment,I need to deal with one button click event to next fragment(B),
then in Fragment,I processing then:
/******************************************************/
getSupportFragmentManager().beginTransaction().addToBackStack(null).replace(R.id.common_top,B);
/******************************************************/
Fouth,now B fragment is in the top,When I press the return key, the current fragment's order is
B->A->homeFragment,there is not problem with the above four stops;
But in the second step,if you replace fragment without call addToBackStack(null) method,like this:
getSupportFragmentManager().beginTransaction().replace(R.id.common_top, A);
When the top fragment is B,When I press the return key, the current fragment's order is
B->homeFragment accourding to Google's official Android documentation,But is not consistent with what I expected。
Is anybody call tell me why? How do I solve this problem?
thans a lot.