I've setup a CoordinatorLayout with a CollapsingToolbar and a RecyclerView in a fragment as so:

```
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/wholeCoordinatorLayout"
android:animateLayoutChanges="true"
android:background="@color/my_background">
<android.support.design.widget.AppBarLayout
    android:id="@+id/myAppBarLayout"
    android:layout_width="match_parent"
    android:layout_height="@dimen/expanded_height"
    android:fitsSystemWindows="true"
    android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">
    <android.support.design.widget.CollapsingToolbarLayout
        android:id="@+id/collapsingToolbar"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:fitsSystemWindows="true"
        app:contentScrim="@color/collapsed_color"
        app:expandedTitleMarginBottom="12dp"
        app:expandedTitleTextAppearance="@style/TransparentText"
        app:collapsedTitleTextAppearance="@style/CollapsedAppBar"
        app:expandedTitleGravity="top|center_horizontal"
        app:collapsedTitleGravity="center"
        app:layout_scrollFlags="scroll|exitUntilCollapsed">
        <ImageView
            android:id="@+id/bannerBgImage"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:src="@drawable/banner_bg"
            android:fitsSystemWindows="true"
            app:layout_collapseMode="parallax"
            android:scaleType="centerCrop" />
        <LinearLayout
            android:id="@+id/headerTextLayout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:gravity="center_vertical"
            android:minHeight="@dimen/collapsed_height"
            android:orientation="vertical"
            app:layout_collapseMode="parallax"
            android:paddingTop="10dp">
            <TextView
                android:id="@+id/headerLabel"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="10dp"
                android:text="@string/title"
                android:textSize="20dp"
                android:textAppearance="?android:attr/textAppearanceMedium"
                android:textStyle="bold"
                fontPath="@string/bold_font"
                android:textColor="@color/my_text_color"
                android:layout_gravity="center_horizontal"
                android:gravity="center" />
            <TextView
                android:id="@+id/mainLabel"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginTop="16dp"
                android:text="@string/text_main"
                android:textSize="15dp"
                android:textAppearance="?android:attr/textAppearanceMedium"
                android:textColor="@color/my_text_color"
                android:layout_gravity="center_horizontal"
                android:gravity="center" />
            <Button
                android:id="@+id/expandedButton"
                android:layout_width="match_parent"
                android:layout_height="40dp"
                android:layout_marginTop="18dp"
                android:layout_marginLeft="60dp"
                android:layout_marginRight="60dp"
                android:background="@drawable/my_button"
                android:text="@string/button_text"
                android:textSize="15dp"
                android:textAppearance="?android:attr/textAppearanceMedium"
                android:layout_gravity="center_horizontal"
                android:gravity="center"
                android:textColor="@color/button_text_color" />
        </LinearLayout>
        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="@dimen/collapsed_height"
            android:layout_gravity="top"
            app:layout_scrollFlags="scroll|enterAlways" />
    </android.support.design.widget.CollapsingToolbarLayout>
</android.support.design.widget.AppBarLayout>
<include
    layout="@layout/recycler_listview" />
</android.support.design.widget.CoordinatorLayout>

```

All works ok and I can scroll up and down and my toolbar expands and collapses.

However:

At certain points in my app lifetime, the data changes in the list (shown in the RecyclerView). I have a listener in my RacyclerView.ListAdapter, and when it registers a data change it calls `NotifyDataSetChanged` to update the list. When this happens, my list redraws (of course) but for some reason it redraws OVER the collapsing toolbar. I wasn't sure this was happening, because my toolbar just disappeared, but when I changed the LinearListAdapter to a GridListAdapter, I could see the toolbar behind the grid items. As soon as I start scrolling a bit, the list rights itself with the toolbar above the list - but I want to stop this happening. Does anyone have a clue what magic I need?

I've overridden the `RecyclerView.AdapterDataObserver` so I can do stuff when the notification comes in...the question is what?