Key Press Queuing

I've noticed when I use C# code to move a game object in response to a keypress, that holding the key down for a few seconds nonstop causes the object to continue moving for a moment after I release the key.

Alternatively, if I just jab the keys quickly, the object starts and stops instantly.

Is this some kind of key queuing and can it be disabled?

Here's the basic code I used to do the move (Spuddie is just a sphere with "arms" along it's axes):

public class SpuddieMover : MonoBehaviour { public GameObject Spuddie;

 private void Update()
 {
     float z = Input.GetAxis("Vertical");
     if ( z > 0)
         Spuddie.transform.Translate(Spuddie.transform.up * Time.deltaTime);
     else if (z < 0)
         Spuddie.transform.Translate(Spuddie.transform.up * Time.deltaTime * -1);
 }

}

Thanks in advance for any help! :)