[Physic] The ball isn't bouncing if the impact angle is too low

Hi guys, I’m new to Unity and it’s probably a silly question, but I have this problem :

alt text

My wall is a static collider, the ball has a ridigbody.
They both have the same material with a bouciness of 1

The ball ball rotation is constraint in every direction, but the result is the same if it’s not. And it’s constraint in the Y axis.

What’s wrong ? Is it the way it’s suppose to be ? Because it will be a problem if the ball sticks to the wall like that

Well, there isn’t much code…

The only line is the one that gets the ball moving :

void Start () {
	rigidbody.AddRelativeForce (new Vector3 (-speed/2, 0, -speed));
}