Android : TextView text is not centered after changing background resource

I have a TextView in a layout defined like so...

<TextView
    android:id="@+id/startworkout"
    android:layout_width="110dip"
    android:layout_height="30dip"
    android:background="@drawable/shape_doworkout_blue_white"
    android:ellipsize="end"
    android:gravity="center"
    android:paddingBottom="4dip"
    android:paddingTop="4dip"
    android:singleLine="true"
    android:text="Do workout"
    android:textColor="@color/blue"
    android:textSize="14sp" />

The background drawable is defined like so...

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android" >

    <item>
        <shape android:shape="rectangle" >
            <solid android:color="@color/blue" />

            <padding
                android:bottom="2dp"
                android:left="2dp"
                android:right="2dp"
                android:top="2dp" />

            <corners
                android:bottomLeftRadius="15dip"
                android:bottomRightRadius="15dip"
                android:topLeftRadius="15dp"
                android:topRightRadius="15dip" />
        </shape>
    </item>
    <item>
        <shape android:shape="rectangle" >
            <padding
                android:bottom="5dp"
                android:left="5dp"
                android:right="5dp"
                android:top="5dp" />

            <corners
                android:bottomLeftRadius="15dip"
                android:bottomRightRadius="15dip"
                android:topLeftRadius="15dp"
                android:topRightRadius="15dip" />

            <solid android:color="@color/white" />
        </shape>
    </item>

</layer-list>

I have another drawable called shape_doworkout_green_white which is the exact same as the above drawable, but @color/blue is replaced with @color/green.

When this TextView displays on screen, everything is how I want it. Most notably, the text is centered.

However, if I update the background resource to my other drawable (or even the same blue drawable), the text becomes slightly off centered.

holder.txtStartWorkout.setBackgroundResource(R.drawable.shape_doworkout_green_white);
holder.txtStartWorkout.setTextColor(getResources().getColor(R.color.green));
holder.txtStartWorkout.setText("Completed");

I'm not sure why this is happening. Ideas?