Delay before first touch position changes on iPhone

I have a problem using Input.touches[0].position. Sorry if the problem is unclear, I find it somewhat hard to describe.

When I start touching the screen and very slowly start to move my finger the position returned by Input.touches[0].position doesn't change immediatly, I have to move a little then it jumps to the current touch position.

This happens on iPhone, I don't have any other touch devices.

Here is some testable code illustrating it:

 using System;
 using UnityEngine;

 // attach this to a game object on the scene
 public class TestTouch : MonoBehaviour
 {
     private void Update()
     {
         if (Input.touchCount == 1)
         {
             // you have to add a GUIText component to the gameobject
             this.guiText.text = "pos: " + Input.touches[0].position;
         }
     }
 }