Having problem with itween.moveto and oreinttopath

Hello, I need help with itween.moveto. I want to shoot an arrow on a parabolic path. I've made the arrow sprite as a child of an empty game object. Both are prefabs. I want the arrow to follow and point the path. I'm using itween.moveto with orienttopath true. The problem is that it is also changing the X and Y rotation values. I want the parabolic path around Z axis only, as it is a 2D game. I've tried using looktime and lookahead but they dont work. The X and Y values of the rotation are still getting modified. Also, i've checked my code thoroughly to see if there is any place where the rotation values are getting modified. But they are not. So can someone plz lemme knw if m doing something wrong or if theres anything else i should do to get the result. Following is the code.

using UnityEngine;
using System.Collections;

public class ProjectileMovement : MonoBehaviour {

 private Transform player;
 private Vector3[] proj_path = new Vector3[3];

// private float lobHeight;
public float lobTime = 2f;

 // Use this for initialization
 void Start () {    

     player = GameObject.Find("Old King").transform;
     proj_path[0] = transform.position;
     proj_path[1] = transform.position + new Vector3((player.transform.position.x - transform.position.x)/2, 3, 0);
     proj_path[2] = player.transform.position;

 
     iTween.MoveTo(gameObject, iTween.Hash("path", proj_path, "time", lobTime, "orienttopath", true, "easetype",iTween.EaseType.linear));
 
 }
 
 // Update is called once per frame
 void Update () {
 
 
 }

}