All the script stoped the update func when i lock the computer

Hi guys; our company has an project which is about going to finish。But recently we found a problem. the unity version we used is 4.3.4.we found that when we lock the windows for a while and unlock it , the game begain at the time we locked the computer.And in the building setting inspector,we made the RunInBackground toggle checked. we write an test script as blew, when we locked the windows ,the count stopped counting.that means the update func has stopped working.we test this code at unity 4.1.2 it works well. but 4.3.4-4.6.4 does not work.we also tested it in unity 5.1.2 and it works..but if the whole project upgrade to UNITY5 ,the work we should do is huge. so,is anyone has the same problem? and how can i fix it with no big change(or upgrade)?

 using UnityEngine;
 using System.Collections;
 
 public class Test1 : MonoBehaviour {
     int[] t = new int[10];
     // Use this for initialization
     void Start () {
     
     }
     
     // Update is called once per frame
     void Update () {
         Debug.LogError("Update");
         t[0]++;
     }
     void LateUpdate()
     {
         Debug.LogError("LateUpdate");
         t[1]++;
     }
     void OnDisable()
     {
         Debug.LogError("OnDisable");
     }
     void OnEnable()
     {
         Debug.LogError("OnEnable");
     }
     void FixedUpdate()
     {
         Debug.LogError("FixedUpdate");
     }
     void OnApplicationPause(bool pause)
     {
         Debug.LogError("OnApplicationPause (" + pause + ")");
     }
     void OnGUI()
     {
         Debug.LogError("OnGUI");
         t[2]++;
 
         GUILayout.Label(t[0]+", " + t[1] + ", " + t[2] + ": \t(" + Time.realtimeSinceStartup + ") \t(" + Time.time + ")");
         GUILayout.Label("Mouse Position: " + Input.mousePosition);
         GUILayout.Label("Screnn Size: " + Screen.width + " * " + Screen.height);
     }
 }