Stock button is shown transparent instead of solid on Honeycomb only

Question

I am using the standard buttons in my activities. On tablets with Honeycomg the Buttons are shown transparent (as they look when they are disabled), but they are enabled and also clickable. So they are still funktional but transparent. Only one togglebutton that I use is shown correctly. How can I get rid of the transparency? Frank

Main-XML (part of it):

<ScrollView
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="@drawable/backrepeat7">
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical"
android:paddingLeft="10dip"
android:visibility="visible" >

<Button
    android:id="@+id/bt_fahrt_erfassen"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:enabled="true"
    android:text="@string/bt_fahrt_erfassen"
    android:visibility="visible" >
</Button>

Backrepeat7.xml:

<bitmap xmlns:android="http://schemas.android.com/apk/res/android" android:src="@drawable/background" android:tileMode="repeat"/>