According to the android documentation for custom animation:
Change:
ft.setCustomAnimations(R.anim.slide_in, R.anim.hyperspace_out);
To:
ft.setCustomAnimations(R.anim.slide_in, R.anim.hyperspace_out, R.anim.hyperspace_in, R.anim.slide_out );
and now the backstack animates – In reverse!!