Android RecyclerView Spacing Differences between Platforms

Disclosure up front, this is a school project.

I've run into a somewhat confusing-to-me layout issue regarding a list of CardViews inside of a RecyclerView, that being that the spacing between cards is non-existent on 5.0, whereas it's fine on 4.4. Here's two screenshots to demonstrate.

Android 4.4 (On Device, Galaxy S4)

Android 5.0.1 (On Device, Nexus 4)

I can see the card corners in the 5.x version, so the cards are there. I have a feeling this is something to do with some XML attribute that I need for running 5.x that the support library fakes automatically on 4.x, but googling has failed me. Here's the relevant XML:

Fragment Layout

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://ift.tt/nIICcg"
xmlns:tools="http://ift.tt/LrGmb4" android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.hinodesoftworks.kanagt.HiraganaListFragment">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/hira_list"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        />
</FrameLayout>

Card Layout

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView xmlns:android="http://ift.tt/nIICcg"
    xmlns:card_view="http://ift.tt/GEGVYd"
    android:layout_height="match_parent"
    android:layout_width="match_parent"
    card_view:cardCornerRadius="4dp">

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <TextView
            android:id="@+id/kana_card_display"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textSize="46sp"
            android:text="あ"/>

        <TextView
            android:id="@+id/kana_card_roma"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_toRightOf="@id/kana_card_display"
            android:layout_toEndOf="@id/kana_card_display"
            android:text="a"
            />

        <TextView
            android:id="@+id/kana_card_info1_display"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_toRightOf="@id/kana_card_display"
            android:layout_toEndOf="@id/kana_card_display"
            android:layout_below="@id/kana_card_roma"
            android:text="INFO 1"/>

        <TextView
            android:id="@+id/kana_card_info2_display"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_toRightOf="@id/kana_card_display"
            android:layout_toEndOf="@id/kana_card_display"
            android:layout_below="@id/kana_card_info1_display"
            android:text="INFO 2"/>

    <HorizontalScrollView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/kana_card_info2_display">
            <ImageView
                android:id="@+id/kana_card_diagram"
                android:layout_width="match_parent"
                android:layout_height="100dp"
                android:scaleType="fitStart"

                android:adjustViewBounds="true"/>
    </HorizontalScrollView>
    </RelativeLayout>

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

I'm really hoping this is a dumb mistake with a simple XML fix; that the support library version is working fine makes me hopeful of that.