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.