Whats wrong with AddTorque and compound colliders ?

I make Rigidbody with compouded box colliders as childs and constraint everything except Y rotation

Have a c# script which apply AddTorque to rigidbody

public class Rotator : MonoBehaviour {

Rigidbody rb;

void Start () {
	rb = GetComponent<Rigidbody> ();	

void OnMouseDown (){
	rb.AddTorque (0,20f,0);


I apply addTorque and expect rigidbody will rotate around world-Y-axis.
But in some cases rotation is magicaly affected (See fig.)

Reproduced in 5.0, 5.3, 5.4, 5.5 Unity

Normaly worked in 4.6

Is it bug?

Ok. Solution found. Need to reset inertiaTensorRotation like this Unity - Scripting API: Rigidbody.inertiaTensorRotation
and all perfectly work