Abnormal Behavior with RadioButton

I am using RadioButton in my layout. Where i have provided background to the RadioButton. Below is the code

<RadioGroup
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    android:orientation="horizontal">

    <RadioButton
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:button="@null"
        android:background="@drawable/rb_spain"
        android:id="@+id/am_rb_spain" />

    <RadioButton
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:button="@null"
        android:background="@drawable/rb_germany"
        android:layout_marginLeft="@dimen/margin_15"
        android:layout_marginRight="@dimen/margin_15"
        android:id="@+id/am_rb_german" />

    <RadioButton
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:button="@null"
        android:background="@drawable/rb_english"
        android:id="@+id/am_rb_english" />

</RadioGroup>

RadioButton background drawable

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://ift.tt/nIICcg" >
    <item android:state_checked="false" android:drawable="@drawable/ic_spain" />
    <item android:state_checked="true" android:drawable="@drawable/ic_spain_pressed" /> //pressed image is Large in size
    <item android:drawable="@drawable/ic_spain" /> <!-- default -->
</selector>

I have saved the selection in TinyDB so that app will remember my selection whenever i open my app. But whenever i open my app the default selected RadioButton background Appears Large. I have taken all the images of same size in drawable's with same padding.

First flag is Default selected here. But it appear to be slightly large in size

Now i have pressed 2nd flag. But first flag is not coming to its normal state.