Fragment replace issue

Main.java

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    if (savedInstanceState == null) {
        ssf = new StartStopFragment();
        tkf = new TimeKeeperFragment();
        rf = new ResetFragment();
        lcf = new LapCounterFragment();
    } else {
        ssf = (StartStopFragment) getFragmentManager().findFragmentByTag(StartStopFragment.class.getName());
        tkf = (TimeKeeperFragment) getFragmentManager().findFragmentByTag(TimeKeeperFragment.class.getName());
        rf = (ResetFragment) getFragmentManager().findFragmentByTag(ResetFragment.class.getName());
        lcf = (LapCounterFragment) getFragmentManager().findFragmentByTag(LapCounterFragment.class.getName());
    }

    getFragmentManager().beginTransaction()
            .replace(R.id.flStartFrame, ssf, StartStopFragment.class.getName())
            .replace(R.id.flTimeKeeperFrame, tkf, TimeKeeperFragment.class.getName())
            .replace(R.id.flResetFrame, rf, ResetFragment.class.getName())
            .replace(R.id.flLapCounterFrame, lcf, LapCounterFragment.class.getName())
            .commit();
}

main.xml

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:baselineAligned="false">
    <LinearLayout
        android:id="@+id/llTopContainer"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight=".4"
        android:orientation="horizontal"
        android:baselineAligned="false">
        <FrameLayout
            android:id="@+id/flResetFrame"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight=".5"
            tools:layout="@layout/fragment_reset"/>
        <FrameLayout
            android:id="@+id/flLapCounterFrame"
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight=".5"
            tools:layout="@layout/fragment_lapcount"/>
    </LinearLayout>
    <FrameLayout
        android:id="@+id/flTimeKeeperFrame"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight=".2"
        tools:layout="@layout/fragment_time"/>
    <FrameLayout
        android:id="@+id/flStartFrame"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight=".4"
        tools:layout="@layout/fragment_startstop"/>
</LinearLayout>