Blank page is shown when pop the fragment & replace to the same fragment again

Question

I have 3 fragments, Frag_A, Frag_B & Frag_C.

My navigation logic is: Frag_A ==> Frag_B ==> Frag_C . That's Frag_A is added into layout firstly, so, at the first time, Frag_A is shown on screen, then, if user press the Next Button, Frag_A is replaced by Frag_B, now Frag_B is shown on screen, if user press the Next button, Frag_B is replaced by Frag_C, so that Frag_C is shown on screen.

Everything works fine with my code at this point.

Method to change to next fragment:

//here, argument 'fragment' is either Frag_B or Frag_C
public void showFragment(Fragment fragment){
   FragmentManager fragMgr = activity.getSupportFragmentManager();
  FragmentTransaction fragTrans = fragMgr.beginTransaction();

  fragTrans.replace(R.id.frag_placeholder, fragment, fragmentName);
  fragTrans.addToBackStack(null);

  int transId = fragTrans.commit();
  fragMgr.executePendingTransactions();

}

Layout file of activity (Frag_A is added to the frag_placeholder when Activity starts):

<?xml version="1.0" encoding="utf-8"?>
<merge xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" 
    >

     <FrameLayout 
        android:id="@+id/frag_placeholder"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
      />
</merge>

But, after Frag_C is shown, if I pop Frag_C by press the physical back button and invoke the showFragment(Frag_C) method to show the Frag_C again right after my code detected the physical button is pressed, I get a blank page shown on screen. Why & how to fix it?

================Explain=====================

I said above "*show the Frag_C again right after my code detected the physical button is pressed*", here is what I mean:

In Activity:

@Override
public void onBackPressed() {
  super.onBackPressed();
  //I detect the Physical Back button is pressed & invoke the method to show the popped Frag_C again.
}

Answer 1

Based on @ Luksprog 's comment, I found that if I create a new instance of Frag_C instead of always use the same instance, the blank page problem get fixed.