Bug GetUIVertexStream not giving correct vertex positions?

I am doing a simple script that is based of the UI Image component in an attempt to something with the vertices of the image object. To that end I use the IMeshModifier so I can use the ModifyMesh(VertexHelper vh) function. All works fine I can get the image showing in Unity and ModifyMesh is called and it gives me 4 vertices as expected but vertex 3 and 4 are the same value which is clearly not true for a quad.
Here is a screenshot showing the output of the script below and you can see the last two values are the same.

And the simple script.

Code (CSharp):

1. using UnityEngine;
2. using UnityEngine.UI;
3. using System.Collections.Generic;
4.  
5. [ExecuteInEditMode]
6. public class BendUI : Image, IMeshModifier
7. {
8.     public GameObject    uiObj;
9.  
10.     public void ModifyMesh(Mesh mesh)
11.     {
12.     }
13.  
14.     public void ModifyMesh(VertexHelper vh)
15.     {
16.         Debug.Log("mod mesh vh count " + vh.currentVertCount);
17.  
18.         List<UIVertex> verts = new List<UIVertex>();
19.         vh.GetUIVertexStream(verts);
20.  
21.         for ( int i = 0; i < vh.currentVertCount; i++ )
22.         {
23.             Debug.Log(i + " " + verts[i].position);
24.         }
25.     }
26. }

Is this a known bug or have I done something wrong? Can't see what it is a very simple script.