LineRenderer animates something strange in Unity 5.5.0b2

I executed below code for checking LineRenderer behavior in Unity 5.5.0b2.

Code (CSharp):

1. using UnityEngine;
2. using UnityEngine.Rendering;
3.  
4. public class MainController : MonoBehaviour
5. {
6.     private LineRenderer _line;
7.  
8.     void Start ()
9.     {
10.         _line = gameObject.AddComponent<LineRenderer>();
11.  
12.         _line.shadowCastingMode = ShadowCastingMode.Off;
13.         _line.receiveShadows = false;
14.  
15.         var mat = new Material(Shader.Find("VR/SpatialMapping/Wireframe"));
16.         _line.sharedMaterial = mat;
17.  
18.         float width = 0.5f;
19.         _line.startWidth = width;
20.         _line.endWidth = width;
21.         _line.SetVertexCount(3);
22.  
23.         _line.numCapVertices = 0;
24.         _line.numCornerVertices = 0;
25.     }
26.    
27.     void Update ()
28.     {
29.         // Loop1();
30.         // Loop2();
31.         Loop3();
32.     }
33.  
34.     void Loop1()
35.     {
36.         float v = Mathf.Sin(Time.time);
37.         _line.SetPosition(0, new Vector3(-1, 0, 0));
38.         _line.SetPosition(1, new Vector3(0, v, 0));
39.         _line.SetPosition(2, new Vector3(1, 0, 0));
40.     }
41.  
42.     void Loop2()
43.     {
44.         float v = Mathf.Sin(Time.time);
45.         _line.SetPosition(0, new Vector3(-1 + v, -1, 0));
46.         _line.SetPosition(1, new Vector3(0, 1, 0));
47.         _line.SetPosition(2, new Vector3(1 - v, -1, 0));
48.     }
49.  
50.     void Loop3()
51.     {
52.         float v = Mathf.Sin(Time.time);
53.         _line.SetPosition(0, new Vector3(-1 , -1, 0));
54.         _line.SetPosition(1, new Vector3(0, 1, 0));
55.         _line.SetPosition(2, new Vector3(1 - v*2.5f, -1, 0));
56.     }
57. }

In the case of Loop1(), the result is attached `1.gif`.
Center corner moves jerkily.

In the case of Loop2(), the result is attached `2.gif`.
Though the center point is fixed in code, but it moving. I think it should not move.

In the case of Loop3(), the result is attached `3.gif`.
Right arm transforms from rectangle to triangle suddenly. I think it should not transform triangle.

 

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