I moved 9-patch files from /drawable to /drawable-hdpi because the error log recommended to use drawable-* to offer density optimized images.
The problem is, that the AppWidget now looks different. When Drawables are stored in /drawable-hdpi the border is thicker.
For more information compare the attached screenshots. What is the reason for this difference?
Screenshot

Layout
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/widget_parent"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="@drawable/widget_bg" >
<TextView
android:id="@+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"
android:text="@string/widget_loading"
android:textAppearance="?android:attr/textAppearanceMedium" />
<ProgressBar
style="?android:attr/progressBarStyleSmall"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerVertical="true"
android:layout_marginRight="4dp"
android:layout_toLeftOf="@+id/textView1" />
</RelativeLayout>
Drawable @drawable/widget_bg_default

widget_bg (stored in /drawables)
<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
<item android:drawable="@drawable/widget_bg_default" android:state_focused="false" android:state_pressed="false" android:state_selected="false"/>
<item android:drawable="@drawable/widget_bg_pressed" android:state_pressed="true"/>
<item android:drawable="@drawable/ic_launcher" android:state_selected="true"/>
<item android:drawable="@drawable/widget_bg_focused" android:state_focused="true"/>
</selector>