[Beta 21] Changing HingeJoint.motor has no effect

I experimented with a box and 4 connected cylinders, all connected to it with a hinge joint.
When I change the motor from the editor, the vehicle starts moving - however, changing it dependent on keys at runtime via C# script has no effect.

Complete project: https://www.dropbox.com/s/ov1s2h7a38mjkvf/Physics-Sandbox.7z?dl=0

Code (CSharp):

1. public class WheelMotor : MonoBehaviour {
2.  
3.     public KeyCode ForwardKey = KeyCode.UpArrow;
4.     public KeyCode BackwardKey = KeyCode.DownArrow;
5.     public float Force = 25.0f;
6.     public float TargetVelocity = 150;
7.  
8.     private HingeJoint hingeJoint;
9.  
10.     // Use this for initialization
11.     public void Start() {
12.         hingeJoint = GetComponent<HingeJoint>();
13.         hingeJoint.useMotor = true;
14.     }
15.    
16.     // Update is called once per frame
17.     public void FixedUpdate () {
18.         if (hingeJoint != null) {
19.             var motor = hingeJoint.motor;
20.             var apply = false;
21.  
22.             if (Input.GetKeyUp(ForwardKey)) {
23.                 motor.targetVelocity = 0;
24.                 apply = true;
25.             } else if (Input.GetKeyUp(BackwardKey)) {
26.                 motor.targetVelocity = 0;
27.                 apply = true;
28.             }
29.  
30.             if (Input.GetKeyDown(ForwardKey)) {
31.                 motor.targetVelocity = TargetVelocity;
32.                 apply = true;
33.             } else if (Input.GetKeyDown(BackwardKey)) {
34.                 motor.targetVelocity = -TargetVelocity;
35.                 apply = true;
36.             }
37.  
38.             if (apply) {
39.                 hingeJoint.motor = motor;
40.             }
41.            
42.         }
43.     }
44. }
45.