How come the behavior of drawableStart doesn't match the Android documentation?

I have created a very basic layout:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >

        <Button
            android:id="@+id/button1"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Button"
            android:drawableStart="@drawable/ic_launcher" />

    </LinearLayout>
</RelativeLayout>

According to the documentation for drawableStart,

"The drawable to be drawn to the start of the text."

However, when run on my Android 4.0.4 phone, I instead see this:

Why is there such a large gap between the icon and the text? According to this answer,

"With Android 4.0 (API level 14) you can use android:drawableStart attribute to place a drawable at the start of the text."

But this is not the behavior I observe. Why isn't the attribute working?