SimpleMove() error, jump by itself

i have a script to make a character move by it self to a certain position. i use simpleMove() to make this character move ignoring the y transition, but when the character reach the target position, it jumps for nothing, when i do a debugging, it shown that the y axis change by it self, anyone knows why..??. when i just change the character posisition manually it works flawlessly. but the physics won't work...

 class AStarAI : MonoBehaviour
 {
     CharacterController cc;
     public bool triggered = false;
     public Transform[] patrolList;    
     public float waypointRadius = 1.5f;
     public bool loop = false;    
     public bool faceHeading = true;
     public float maxSpeed = 10f;
     public float maxTurningSpeed = 360f;
     public float acceleration = 3f;
     public float proximityRadius = 3f;
     float speed = 0f;
 
     private WayPointsCollector WPcol;
     private Transform[] CurrentWaypoints;
     private Vector3 targetHeading;
     private Vector3 direction;
     private int targetwaypoint;
        
 
     void Start(){
         WPcol = (WayPointsCollector)GameObject.FindWithTag("walkable").GetComponent("WayPointsCollector");        
         CurrentWaypoints = new Transform[patrolList.Length];
         patrolList.CopyTo(CurrentWaypoints,0);
 
         if (CurrentWaypoints.Length <= 0)
         {
             //Debug.Log("No waypoints on " + name);
             enabled = false;
         }
         targetwaypoint = 0;
         cc = GetComponent<CharacterController>();   
         
     }
 
     void FixedUpdate()
     {
         targetHeading = (CurrentWaypoints[targetwaypoint].position - transform.position);   
     }
 
     void Update() {
         if (!triggered) {           
         }
         else {            
         }
 
         targetHeading.y = 0f;
         bool turned = false;
         // Do we need to adjust facing?
         Quaternion idealFacing = Quaternion.LookRotation(targetHeading);
         // This is how far we would like to turn
         float angle = Quaternion.Angle(transform.rotation, idealFacing);
         
         // This is most we are allowed to turn this frame
         float maxTurn = maxTurningSpeed * Time.deltaTime;
         if (maxTurn >= angle)
         {
             // Excellent. We can just face the target            
             transform.Rotate(0, angle, 0);
         }
         else
         {
             // We'll have to take this more gradually then; use slerp to smoothly face the target.            
             transform.Rotate(0, maxTurn, 0);
             turned = true;
         }
 
         // Now that we've adjusted facing, let's move our wanderer around
         if (turned)
         {
             // If we needed to turn then slow down while we correct course, bringing ourselves to a halt if necessary.
             speed = Mathf.Max(0f, speed - acceleration * Time.deltaTime);
         }
         else
         {
             // Since we didn't turn we will speed up if the target is far away and slow down otherwise
             float distance = targetHeading.magnitude;
             if (distance > proximityRadius)
             {
                 speed = Mathf.Min(maxSpeed, speed + acceleration * Time.deltaTime);
             }
             else
             {
                 float frac = distance / proximityRadius;
                 float idealSpeed = maxSpeed * frac;
                 speed = Mathf.Max(idealSpeed, speed - acceleration * Time.deltaTime);
             }
             // Close enough? Then go somewhere else.
             if (Vector3.Distance(transform.position, CurrentWaypoints[targetwaypoint].position) <= waypointRadius)
             {
                 targetwaypoint++;
                 if (targetwaypoint >= CurrentWaypoints.Length)
                 {
                     targetwaypoint = 0;
                     if (!loop)
                         enabled = false;
                 }
             }
         }
         
         // Move.
         cc.SimpleMove(transform.forward * speed);
         //transform.position += transform.forward * speed * Time.deltaTime;
         
     }
 }

thx.