I have some custom class BitmapStorage, not attached to any View or whatever - an utility one.
And I have born_animation.xml file which contains
Yay, I found the cause! :)
It was my bad: I didn't had the proper format of my animation.xml file:
After I fixed these things res.getDrawable() started to return a correct AnimationDrawable instance.
Had to look more precisely at Resources.NotFoundException and it's getCause() to find out what's wrong :)