NGUI 3.5.1 only update yesterday. Have tried on web, android and iOS, all them same. Steps taken to reproduce
Unity -> New Project
Only import NGUI
Create label
add collider
add button script
add my script
set notify
run
My script
using UnityEngine;
using System.Collections;
public class tstScript : MonoBehaviour
{
public void OnClick()
{
Debug.Log("You clicked");
}
}