Sprite occasionally moving to left when dragging to right

Below is the code that I use to drag my sprite along the x-axis. Occasionally the sprite just quickly moves to the left end when I am moving it right. I would like to know what is causing the inconsistent behaviour in dragging the sprite. Please see the code:

 public class dragSprite : MonoBehaviour {
     Vector3 startPosition;
         Transform cachedTransform;
     float horizontalLimit = 2.5f, dragSpeed = 0.01f;
 
     void Start () {
         startPosition = camera.ScreenToWorldPoint(new Vector3(Screen.width/2, Screen.Height/2, camera.nearClipPlane));
         transform.position = startPosition;
         cachedTransform = transform;
 }
 
     void Update () {
         if (Input.touchCount > 0) {
             Vector2 deltaPosition = Input.GetTouch(0).deltaPosition;
             switch(Input.GetTouch(0).phase)    {
 
             case TouchPhase.Began:
                 break;
 
             case TouchPhase.Moved:
                 drag(deltaPosition);
                 Debug.Log("touchPhase moved");
                 break;
 
             case TouchPhase.Ended:
                 break;
 
             }
         }
     }
 
     void drag(Vector2 deltaPosition)    {
 
         cachedTransform.position = new Vector3 (
             Mathf.Clamp ((deltaPosition.x * dragSpeed) + cachedTransform.position.x, startPosition.x - horizontalLimit, startPosition.x + horizontalLimit),
         startPosition.y,
             cachedTransform.position.z);
     }
 }