Unexpected RadioButton behavior

Here is my layout: ``` <?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent" android:background="#FFFFFFFF"> <RadioGroup android:id="@+id/choices_group" android:layout_width="fill_parent" android:layout_height="wrap_content" android:layout_margin="5dp" android:layout_centerInParent="true" android:orientation="vertical" android:background="@drawable/rounded_bg" > <RadioButton android:id="@+id/choice_a" android:layout_width="fill_parent" android:layout_height="wrap_content" android:gravity="center_vertical" android:padding="5dp" android:text="Choice A" /> <RadioButton android:id="@+id/choice_b" android:layout_width="fill_parent" android:layout_height="wrap_content" android:padding="5dp" android:text="Choice B" /> <RadioButton android:id="@+id/choice_c" android:layout_width="fill_parent" android:layout_height="wrap_content" android:padding="5dp" android:text="Choice C" /> <RadioButton android:id="@+id/choice_d" android:layout_width="fill_parent" android:layout_height="wrap_content" android:padding="5dp" android:text="Choice D" /> </RadioGroup> </RelativeLayout> ``` Why are the radio buttons superimposed over the text?