CardView inserts dark line at bottom
<p>I'm using <code>com.android.support:cardview-v7:23.3.0.</code></p>

<p>On <strong>API &lt; 21</strong> my CardView insists on placing a dark line at the bottom as shown here</p>

<p><a href="https://i.stack.imgur.com/qx4ku.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/qx4ku.jpg" alt="enter image description here"></a></p>

<p>This is my layout.</p>

<pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
&lt;LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:gravity="center"&gt;

&lt;android.support.v7.widget.CardView

    android:id="@+id/category_cardView"
    android:layout_width="320dp"
    android:layout_height="wrap_content"
    android:layout_margin="0dp"
    card_view:cardBackgroundColor="#80d0d0d0"
    card_view:cardCornerRadius="30dp"
    card_view:cardUseCompatPadding="true"&gt;

    &lt;RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"&gt;

        &lt;ImageView
            android:id="@+id/list_item_category_imageImageView"
            android:layout_width="50dp"
            android:layout_height="50dp"
            android:layout_margin="3dp"
            tools:ignore="contentDescription"
            tools:src="@drawable/ic_launcher_find_the_fun" /&gt;

        &lt;ImageButton
            android:id="@+id/list_item_category_listButton"
            android:layout_width="50dp"
            android:layout_height="50dp"
            android:layout_alignParentRight="true"
            android:layout_centerVertical="true"
            android:layout_margin="3dp"
            android:background="@drawable/button_selector_category"
            android:contentDescription="@string/cd_list"
            android:padding="10dp"
            android:scaleType="fitXY"
            android:src="@drawable/ic_list_black_24dp" /&gt;

        &lt;ImageButton
            android:id="@+id/list_item_category_mapButton"
            android:layout_width="50dp"
            android:layout_height="50dp"
            android:layout_centerVertical="true"
            android:layout_toLeftOf="@+id/list_item_category_listButton"
            android:background="@drawable/button_selector_category"
            android:contentDescription="@string/cd_map"
            android:padding="10dp"
            android:scaleType="fitXY"
            android:src="@drawable/ic_map_black_24dp" /&gt;

        &lt;!-- Title --&gt;
        &lt;TextView
            android:id="@+id/list_item_category_titleTextView"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerVertical="true"
            android:layout_toLeftOf="@id/list_item_category_mapButton"
            android:layout_toRightOf="@id/list_item_category_imageImageView"
            android:paddingRight="3dp"
            android:textSize="17sp"
            android:textStyle="bold"
            android:typeface="sans"
            tools:text="Category Title" /&gt;
    &lt;/RelativeLayout&gt;
&lt;/android.support.v7.widget.CardView&gt;
</code></pre>

<p></p>

<p>I've tried various things to remove it. If I delete the line containing "card_view:cardCornerRadius="30dp"" here's what I see:</p>

<p><a href="https://i.stack.imgur.com/BeAKb.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/BeAKb.jpg" alt="enter image description here"></a></p>

<p>I see exactly the same as above if I explicitly set <code>card_view:cardCornerRadius="0dp"</code>.</p>

<p>The following variations in my layout do not fix this (I've tried these mainly to debug, not because I really expected them to make a difference).</p>

<ol>
<li>I changed to using card_view:cardUseCompatPadding="false"</li>
<li>card_view:cardUseCompatPadding="true"</li>
<li>card_view:cardPreventCornerOverlap="true"</li>
<li>card_view:cardPreventCornerOverlap="false"</li>
<li>card_view:contentPadding="0dp"</li>
</ol>

<p>Can you suggest what is wrong with this layout or even a debugging step to try?</p>