Android: layer list without animation scaling

Android: layer list without animation scaling

I'm working first time with animation on Android. And I discovered this
fact and I became really angry. I had a template for button with rectangle
as background and an image bitmap centered using layer list. OK, now I
want to replace bitmap image with an animation. I created animation-list
drawable and changed my buttons code:
<layer-list>
<item>
<shape android:shape="rectangle">
<gradient
android:startColor="#666666"
android:endColor="#666666"
android:angle="90"
android:centerY="10%"
/>
<corners android:radius="0dp" />
</shape>
</item>
<item
android:drawable="@drawable/arrowseq">
</item>
There is no possibility to avoid this very anoying auto-scaling like for
bitmap. Could you please help me or explain WHY?
Lot of thanks!