I discovered this issue today, and solved it by doing the following --
1/ Create a text file called styles.xml in ..\objects\res\values
2/ Paste in the following code --
<?xml version="1.0" encoding="utf-8"?>
<resources>
<style name="Theme.Transparent" parent="android:Theme.Holo.Light">
<item name="android:windowNoTitle">true</item>
<item name="android:background">@android:color/transparent</item>
<item name="android:windowBackground">@android:color/transparent</item>
<item name="android:colorBackgroundCacheHint">@null</item>
<item name="android:windowIsTranslucent">true</item>
<item name="android:windowAnimationStyle">@android:style/Animation</item>
</style>
</resources>
3/ Save and make the file read-only.
4/ In your b4a project's manifest editor, use the following --
SetActivityAttribute(YourActivityName, android:theme, @style/Theme.Transparent)