Question Why does animation jump to start at t=1

I need to control the anim frame by frame for a use case in our game. The POC test code looks like

Code (CSharp):

1. public class Test : MonoBehaviour
2. {
3.     public Animator anim;
4.  
5.     [Range(0, 1)]
6.     public float t;
7.  
8.     public void Start()
9.     {
10.         anim.speed = 0;
11.         anim.StopPlayback();
12.     }
13.  
14.     public void Update()
15.     {
16.         anim.Play("EjectCasing", -1, t);
17.        
18.     }
19. }

At T=1 the animation jumps to the first frame

 

Is this by design or a bug? Seems like a bug?