I think it is the way you are calling the event

Code:

---

function init_sphere()

{
my.enable_impact = on;	
my._event = bounce_event;
....
}

function bounce_event()
{
	if(event_type == event_impact)
	{
		//addforce along the BOUNCE vector here or you might want to wait a frame to make sure the ball has already changed course and then just boost it in that direction.
		//experiment)
	}
}  

---