Problem with getting hit raycast position

My script:

     Ray ray = new Ray(transform.position + Vector3.up * 100, Vector3.down);
     RaycastHit hit;

     if (Physics.Raycast(ray, out hit, Mathf.Infinity))
     {
         Debug.Log("HIT: " + hit.collider.name);
         transform.position = hit.point;
     }

but my gameobject just jump off :/ http://scr.hu/3tpn/hesic it just bounce of the ground once and just fly .. But with terrain this script works fine:

 // Update is called once per frame
 void Update()
 {
     Ray ray = new Ray(transform.position + Vector3.up * 100, Vector3.down);
     RaycastHit hit;

     if (terrain.GetComponent<Collider>().Raycast(ray, out hit, Mathf.Infinity))
     {
         Debug.DrawLine(transform.position, hit.point);
         if (rotate)
         {
             transform.position = hit.point + Vector3.up * upCount;
             transform.rotation = Quaternion.FromToRotation(transform.up, hit.normal) * transform.rotation;
         }
         else
         {
             transform.position = hit.point + Vector3.up * upCount;
         }
     }
 }