Android : The rounded corners work different in different Android version

I have problem with the corners tag.

This is my shape file.

<stroke
    android:width="1dp"
    android:color="#ff999999" />

<size android:height="40dp" />

<gradient
    android:angle="90"
    android:centerColor="#f5f5f5"
    android:endColor="#fcfcfc"
    android:startColor="#efefef"
    android:type="linear" />

<corners
    android:bottomLeftRadius="0dip"
    android:bottomRightRadius="8dip"
    android:topLeftRadius="8dip"
    android:topRightRadius="0dip" />

But when I set it for view's background. It display different shape in Android 2.2 and Android 4.0.3 . When it is running on Android 4.0.3 :running on Android 4.0.3 And on Android 2.2 :Running on Android 2.2

Please see "ANNOUNCE" button. Do you know why ? And how can I fix it ? Please help me ! Sorry because my English is not really well.