[android help] FragmenManager replace makes overlay

I'm using supportlib v4 to reach master-detail flow.

Problem: New instance of "details" fragment overlays the first one (xml created) instead replace it.

My Activity layout is:

    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal"
    tools:context=".TrackListActivity" >

            android:id="@+id/fragmentList"
        android:name="pl.com.digita.BikeComputerUi.TrackList.TrackListFragment"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1" />

            android:id="@+id/fragmentTrack"
        android:name="pl.com.digita.BikeComputerUi.TrackList.TrackInfoFragment"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="2" />

Method called after click:

private void showDetails(long trackId){
    View fragmentContainer = getActivity().findViewById(R.id.fragmentTrack);
    TrackInfoFragment trackInfoFragment =  TrackInfoFragment.newInstance(trackId);
    FragmentManager fragmentManager =  getFragmentManager();
    fragmentManager.beginTransaction().replace(fragmentContainer.getId(), trackInfoFragment).commit();

    }

.

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