Thank you! That's the point! I misunderstood OnEnterBack and onLeaveBack meaning.
Now, if I can, i wold ask you another question. How to reset the animation on backscrolling only when the element is outside of the viewport?
It will simply work with toggleActions:"play reset play reset" if only I didn't have that start: 'top 50%', but I want my animations to start a bit after the elemnts get in viewport.