Android on rotation one fragment "cannot be cast to" another fragment

Question

The app is working fine until I rotate the screen. Then the two fragments get confused. Here is the code from the Activity:

private PopupScreen popupFragment;
private PlayerWindow playerWindowFragment;

and after onCreate:

if (savedInstanceState == null) {
        Log.v(TAG, "onCreate: SAVEDINSTANCESTATE IS NULL, NEW ACTIVITY and FRAGMENTS");
        popupFragment = new PopupScreen();
        playerWindowFragment = new PlayerWindow();
        Bundle args = new Bundle();
        args.putInt("defaultBtnImgValue", au);
        args.putInt("btnImg", au);
        popupFragment.setArguments(args);
        playerWindowFragment.setArguments(args);
        FragmentTransaction transaction =
                getSupportFragmentManager().beginTransaction();
        transaction.replace(R.id.popupfragmentframe, popupFragment, POPUPWINDOWFRAME);
        transaction.replace(R.id.playerwindowfragmentframe, playerWindowFragment, PLAYERWINDOWFRAME);
        transaction.commit();
    } else {
        popupFragment = (PopupScreen) getSupportFragmentManager().findFragmentByTag(POPUPWINDOWFRAME);
        playerWindowFragment = (PlayerWindow) getSupportFragmentManager().findFragmentByTag(PLAYERWINDOWFRAME);
    }`

Here is the xml for the activity. The fragments are in a LinearLayout:

<FrameLayout
    android:id="@+id/popupfragmentframe"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">
</FrameLayout>
<FrameLayout
    android:id="@+id/playerwindowfragmentframe"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">
</FrameLayout>

Here is the Log:

Caused by: java.lang.ClassCastException: au.com.packagename.PlayerWindow cannot be cast to au.com.packagename.PopupScreen

When I inflated the popupfragment as a Fragment instead of a FrameLayout in the Activity xml, it was OK.

Thanks for all help.