windowBackground in Android 6 (Marshmallow)

Question

I have defined a base style for my application with the following element:

<item name="android:windowBackground">@color/window_background</item>

Which has set the background color for all my activities fine until I tested my app on Android 6 where all backgrounds are white. The backgrounds are still color/window_background on devices running pre-marshmallow.

Anyone know how to make this work (or why it is not working) on Android 6?

Edit with some more info: I am targeting API 22, I have not changed anything from previous version or upgraded the API, just running on Android 6 changes the background.