title: NavigationView - Setting `app:itemBackground` causes menu items to lose start padding
body: <p>I am running into an issue when setting the <code>app:itemBackground</code> for the NavigationView. I am trying to create a custom background for the selected menu item. The custom background works, but when I use it, it seems to kill the start padding of the menu items.</p>
  
  <p>Without the background(default)</p>
  
  <p><a href="https://i.stack.imgur.com/bVxXU.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/bVxXU.png" alt="enter image description here"></a></p>
  
  <p>With the custom background
  <a href="https://i.stack.imgur.com/FeCvw.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/FeCvw.png" alt="enter image description here"></a></p>
  
  <p>You can see that the menu items are flush to the left of the menu when the <code>itemBackground</code> is set. </p>
  
  <p>Here is the relevant xml...</p>
  
  <p>layout</p>
  
  <pre><code> &lt;android.support.v4.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:id="@+id/DrawerLayout"
      android:fitsSystemWindows="false"&gt;
  &lt;!-- your content layout --&gt;
      &lt;include
          layout="@layout/MainLayout" /&gt;
      &lt;android.support.design.widget.NavigationView
          android:layout_width="wrap_content"
          android:layout_height="match_parent"
          android:layout_gravity="start"
          android:background="@color/primary_color"
          android:id="@+id/NavigationView"
          app:itemTextColor="?android:textColorPrimary"
          app:headerLayout="@layout/navigationheaderlayout"
          app:itemBackground="@drawable/navigation_item_selector"
          app:menu="@menu/navigation_menu" /&gt;
  &lt;/android.support.v4.widget.DrawerLayout&gt;
  </code></pre>
  
  <p>selector</p>
  
  <pre><code>&lt;selector xmlns:android="http://schemas.android.com/apk/res/android"&gt;
     &lt;item android:drawable="@drawable/navigation_item_selected_background" android:state_selected="true" /&gt;
     &lt;item android:drawable="@drawable/navigation_item_selected_background" android:state_pressed="true" /&gt;
     &lt;item android:drawable="@drawable/navigation_item_selected_background" android:state_checked="true" /&gt;
     &lt;item android:drawable="@drawable/navigation_item_not_selected_background" /&gt;
  &lt;/selector&gt;
  </code></pre>
  
  <p>selected backgroud</p>
  
  <pre><code>&lt;layer-list xmlns:android="http://schemas.android.com/apk/res/android" &gt;
      &lt;item 
          android:left="0dp" 
          android:right="2dp" 
          android:drawable="@color/accent_color" /&gt;
  
      &lt;item 
          android:left="2dp" 
          android:right="2dp" 
          android:drawable="@color/navigation_selected_item_color" /&gt;
  &lt;/layer-list&gt;
  </code></pre>
  
  <p>not selected background</p>
  
  <pre><code>&lt;layer-list xmlns:android="http://schemas.android.com/apk/res/android"&gt;
     &lt;item&gt;
         &lt;shape android:shape="rectangle"&gt;
             &lt;solid android:color="@android:color/transparent" /&gt;
         &lt;/shape&gt;
     &lt;/item&gt;
  &lt;/layer-list&gt;
  </code></pre>
  
  <p>Has anybody run into something like this before?</p>