Old fragment is on top after pressing home button mid-animation

Question

I have fragments transitioning in Activity with animation. I noticed that when I press home button while animation is played, and come back using app locker, the fragment I was transitioning from is on top of new one, and is there until activity is finished.

FragmentTransaction transaction = getSupportFragmentManager()
            .beginTransaction();
    if (addTransitionAnimation) {
        transaction.setCustomAnimations(R.anim.enter_from_right, R.anim.exit_to_left);
    }
    transaction
            .replace(R.id.instructions_content, fragment)
            .addToBackStack(null)
            .commit();