setBackgroundDrawable with another view's background drawable selector breaks the selector states
<p>If I set a Drawable object from Button.getBackground() on a button with a selector drawable and then call set setBackgroundDrawable on another button with that same drawable the selector states don't work. </p>

<p>Example:</p>

<pre><code>//layout is inflated from XML

//buttonA object ref set from view
//buttonB object ref set from view

drawableA = buttonA.getBackground();
drawableB = buttonB.getBackground();
</code></pre>

<p>Now calling <code>buttonA.setBackgroundDrawable(drawableB)</code> will result in buttonA not animating correctly in the different selector states. </p>

<p>Am I doing something wrong? I tried calling getConstantState().newDrawable(getResources()).mutate() to make something like a copy of the drawable in case the state was bound to the original button but that didn't seem to help. </p>
