Q:

CoordinatorLayout status bar padding disappears from ViewPager 2nd page

EDIT of 01/02/2016: Bug should be resolved by applying the code provided by Android Team: https://stackoverflow.com/a/35132144/3397345, see accepted answer below.
EDIT of 27/01/2016: Bug still not resolved in v23.1.1. Solutions provided until now don't give transparent status bar (which is the purpose of this layout) or are too complex. A new screen-record of the bug available here: https://www.youtube.com/watch?v=76IxhlUx8MQ 
EDIT of 23/07/2015: Support Design Library v22.2.1 didn't fix :-( Also this happens on toolbar quick return on MainActivity!
EDIT of 28/07/2015: Linked question: CoordinatorLayout status bar padding disappears during fragment transactions
From example repository https://github.com/chrisbanes/cheesesquare I've implemented the ViewPager on Detail Activity. It works, but the StatusBar disappears from 2nd page as you see in the picture only in Lollipop devices, Any idea?
I use android:fitsSystemWindows="true" but it does work only on first page :-(

activity_detail_viewpager.xml
if I put here fitsSystemWindows, StatusBar is not transparent anymore, but it works (status bar padding is not lost). But I would like it transparent!
<android.support.design.widget.CoordinatorLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
        android:id="@+id/main_content"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    <android.support.v4.view.ViewPager
        android:id="@+id/viewpager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:overScrollMode="ifContentScrolls"/>

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

activity_detail_fragment.xml
<CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/main_content"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true">

    <android.support.design.widget.AppBarLayout
        android:id="@+id/appbar"
        android:layout_width="match_parent"
        android:layout_height="@dimen/detail_backdrop_height"
        android:fitsSystemWindows="true"
        android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">

        <android.support.design.widget.CollapsingToolbarLayout
            android:id="@+id/collapsing_toolbar"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:fitsSystemWindows="true"
            app:layout_scrollFlags="scroll|exitUntilCollapsed"
            app:contentScrim="?attr/colorPrimary"
            app:expandedTitleMarginStart="48dp"
            app:expandedTitleMarginEnd="64dp">

            <ImageView
                android:id="@+id/back_item"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:scaleType="centerCrop"
                android:fitsSystemWindows="true"
                app:layout_collapseMode="parallax" />

            <android.support.v7.widget.Toolbar
                android:id="@+id/toolbar"
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize"
                app:popupTheme="@style/ThemeOverlay.AppCompat.Light"
                app:layout_collapseMode="pin" />

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

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

    <android.support.v4.widget.NestedScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical"
            android:paddingTop="24dp">

            <android.support.v7.widget.CardView
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_margin="@dimen/card_margin">

                ...

            </android.support.v7.widget.CardView>

            ...

        </LinearLayout>

    </android.support.v4.widget.NestedScrollView>

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fab"
        android:layout_height="wrap_content"
        android:layout_width="wrap_content"
        android:layout_margin="@dimen/fab_margin"
        android:clickable="true"
        android:src="@drawable/ic_discuss"
        app:layout_anchor="@id/appbar"
        app:layout_anchorGravity="bottom|end"
        app:borderWidth="0dp"/>

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

style.xml v21
<resources>
    <style name="AppTheme" parent="AppTheme.Base">
        <item name="android:windowDrawsSystemBarBackgrounds">true</item>
        <item name="android:statusBarColor">@android:color/transparent</item>
    </style>
</resources>

A:

Solution proposed by Android Team in the answer of my reported defect. This code should finally work.
ViewPager mViewPager;

ViewCompat.setOnApplyWindowInsetsListener(mViewPager,
        new OnApplyWindowInsetsListener() {
    @Override
    public WindowInsetsCompat onApplyWindowInsets(View v,
            WindowInsetsCompat insets) {
        insets = ViewCompat.onApplyWindowInsets(v, insets);
        if (insets.isConsumed()) {
            return insets;
        }

        boolean consumed = false;
        for (int i = 0, count = mViewPager.getChildCount(); i <  count; i++) {
            ViewCompat.dispatchApplyWindowInsets(mViewPager.getChildAt(i), insets);
            if (insets.isConsumed()) {
                consumed = true;
            }
        }
        return consumed ? insets.consumeSystemWindowInsets() : insets;
    }
});

A:

Like sidecarcat, I ran into a similar issue (using v23.1.1).
I post here a workaround by using the code of sidecarcat and add some code to remove superflous padding in some cases.
    // in onCreateView: adjust toolbar padding
    final int initialToolbarHeight = mToolbar.getLayoutParams().height;
    final int initialStatusBarHeight = getStatusBarHeight();
    mToolbar.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
        @Override
        public void onGlobalLayout() {
            int[] locToolbar = new int[2];
            mToolbar.getLocationOnScreen(locToolbar);
            int yToolbar = locToolbar[1];
            int topPaddingToolbar = mToolbar.getPaddingTop();
            if (isAdded()) {
                //normal case : system status bar padding on toolbar : yToolbar = initialStatusBarHeight && topPaddingToolbar = 0
                //abnormal case : no system status bar padding on toolbar -> toolbar behind status bar => add custom padding
                if (yToolbar != initialStatusBarHeight && topPaddingToolbar == 0) {
                    mToolbar.setPadding(0, initialStatusBarHeight, 0, 0);
                    mToolbar.getLayoutParams().height = initialToolbarHeight + initialStatusBarHeight;
                }
                //abnormal case : system status bar padding and custom padding on toolbar -> toolbar with padding too large => remove custom padding
                else if (yToolbar == initialStatusBarHeight && topPaddingToolbar == initialStatusBarHeight) {
                    mToolbar.setPadding(0, 0, 0, 0);
                    mToolbar.getLayoutParams().height = initialToolbarHeight;
                }
            }
        }
    });

    return mRootView;
}

public int getStatusBarHeight() {
    int result = 0;
    int resourceId = getResources().getIdentifier("status_bar_height", "dimen", "android");
    if (resourceId > 0) {
        result = getResources().getDimensionPixelSize(resourceId);
    }
    return result;
}

