if (input.Getkey(Keycode) returns true forever after pressing the key once?

Is this a bug in unity 2019?

  void LateUpdate()
 {
           if (Input.GetKey(KeyCode.LeftShift)) { boostAxis = 1; }//speed up
 }

if you press shift, this if statement returns true forever. However using the input manager:

 void LateUpdate()
 {
       boostAxis = Input.GetAxis("boost buttons"); //speed up
 }

only returns true while the button is held. Is there a way to make "GetKey" work the same way as "GetButton" or "GetAxis" and return true only while held?