Physics + BulletTime = problems

I have got a physical OBJECT A (a skateboarder) attached by joint to a physical OBJECT B (a skateboard). I move OBJECT B using:

 void Update()
 {
     if (tmpSpeed < 4)
     tmpSpeed += 0.01F;

     rigidbody.velocity = new Vector3( 0, 0, tmpSpeed );

When I switch on Bullet-Time:

     Time.timeScale = 0.2F;
     Time.fixedDeltaTime = Time.timeScale * 0.02F;

My OBJECT A (skateboarder) breaks joints with OBJECT B and only then it enters a Bullet-Time mode. As if too late...

I try to change values in TimeManager but it seems nothing has changed.