Sphere sticks to cube

The problem: why does my sphere stick to the lower border after bouncing from the right border?

This problem always happens when ball.rigidbody.velocity.x != 0.

Update: I created a workaround which is shown below.

This is my simple scene (I removed all other parts to ensure that the bug doesn’t relate to my code):

My Physic Material which I applied to both cuboids:

Dynamic Friction:          0
Static Friction:           0
Bounciness:                1
Friction Combine:          Minimum
Bounce Combine:            Maximum
Friction Direction 2:      0, 0, 0
Dynamic Friction 2         0
Static Friction 2:         0

I also created a behavior for the ball which basically sets rigidbody.velocity to an initial motion vector (say 3, -1, 0).

My workaround:
Vector3 velo = rigidbody.velocity;
string[] applicableBorders = new string[]{"BorderTop", "BorderBottom"};

if (velo.x == 0 && System.Array.IndexOf(applicableBorders, collision.collider.name) < 0) {
  rigidbody.velocity = new Vector3(rigidbody.velocity.x, rigidbody.velocity.y * -1.0f, rigidbody.velocity.z);

I wonder whether any cleaner solution exists.

It works now.

I only removed my code - nothing else. That’s really strange because it hasn’t had worked before without the code.