Custom button with drawable background: Padding difference in Android 4 vs. Android 2.3

The following code is for displaying a custom button in Android. Unfortunately, all those padding values at those different places affect the way the button is rendered only for Android 2.3, but on Android 4.X it has no effect, i.e. the padding is always the same, regardless of what you set here. Why?

The layout XML:

<Button
    android:id="@+id/sample_button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/button_caption"
    android:padding="6dp"
    android:layout_marginBottom="6dp"
    android:layout_marginRight="6dp"
    style="@style/CustomButton"
    android:textSize="16sp" />

The style:

<style name="CustomButton">
    <item name="android:layout_gravity">center_horizontal</item>
    <item name="android:padding">6dp</item>
    <item name="android:background">@drawable/custom_button</item>
    <item name="android:textColor">#ffffff</item>
    <item name="android:gravity">center</item>
    <item name="android:textStyle">bold</item>
</style>

The drawable:

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:state_pressed="true">
        <shape>
            <solid
                android:color="#60ff0000" />
            <stroke
                android:width="1dp"
                android:color="#ffffff" />
            <corners
                android:radius="4dp" />
            <padding
                android:left="6dp"
                android:top="6dp"
                android:right="6dp"
                android:bottom="6dp" />
        </shape>
    </item>
    <item>
        <shape>
            <solid
                android:col