Why does my view's background change during an animation?

Simple animation; I just want something to slide away to the left.

<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android">
    <translate android:fromXDelta="0"
               android:toXDelta="-100%"
               android:duration="1000"/>
</set>

I have an ExpandableListView:

<ExpandableListView android:id="@id/android:list"
     开发者_如何学JAVA               android:background="@android:color/transparent"
                    ... />

To which I apply this:

ExpandableListView list = getExpandableListView();
Animation anim = AnimationUtils.loadAnimation(TvEventListActivity.this, R.anim.left);
list.startAnimation(anim);

When I start the animation, the list background, which should be transparent, changes to a solid grey background for the duration of the animation. Then it is restored to correctness.

Why does this happen? How can I prevent it?

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Be sure to set your android:cacheColorHint to transparent if a background Drawable is used or the same background color if a solid color is used.