IssueTracker

Library used (support-v4, appcompat-v7, ...):
Version used:
compile 'com.android.support:design:22.2.0'
compile 'com.android.support:recyclerview-v7:22.2.0'


When setting Toolbar with app:layout_scrollFlags="scroll|enterAlways" as a AppBarLayout only child. There are times where the 'quick return' did not show the Toolbar/AppBar. Displaying a white space.

Found a reproduceable way:
1) Have a Toolbar inside AppBar with app:layout_scrollFlags="scroll|enterAlways" and RecyclerView with  app:layout_behavior="@string/appbar_scrolling_view_behavior" (refer XML below)
2) scroll the AppBar fully away to allow full viewing of RecyclerView
3) Press Home button in the Android NavigationBar
4) Return to the app via Recent App in Android NavigationBar
5) Notice the AppBar still maintains the hidden/scrolled away state
6) Scroll the list to make the AppBar 'quick return'
7) The AppBar is now empty

Note: background of Views has been set a color for demo purpose to identify components

<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.design.widget.AppBarLayout
        android:id="@+id/appbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="#3bd3cb"
        android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar_actionbar"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:background="?colorPrimary"
            android:minHeight="?attr/actionBarSize"
            android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
            app:layout_scrollFlags="scroll|enterAlways"
            app:popupTheme="@style/ThemeOverlay.AppCompat.Light" />

    </android.support.design.widget.AppBarLayout>


    <android.support.v7.widget.RecyclerView
        android:id="@android:id/list"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="#330000cc"
        app:layout_behavior="@string/appbar_scrolling_view_behavior" />

</android.support.design.widget.CoordinatorLayout>