Reflections disappear when changing materials color

I use the Hardsurface shaders by Bruno Rime. I also use a realtime reflection script.

When I change the color of the material (in another script), with Material.SetColor(), the reflections dissappear.

Edit: seems that the refletions disappear even when the script just access the material, even without changing the color...

     foreach(Renderer rend in CarBodyRenderers){
                           foreach(Material matt in rend.materials){
               //  if(matt.name == carBodyMaterialName){
                //         matt.SetColor("_Color", carPaint);
                       }
                }
           }  
 
 // this is the real time reflection script
 
 using UnityEngine;
 using System.Collections;
 
 public class RealtimeCubemap : MonoBehaviour {
 
     public int cubemapSize = 128;
     public bool oneFacePerFrame = false;
     private Camera cam;
     private RenderTexture rtex;
     private GameObject go;
 
     [ExecuteInEditMode]
     void Start() {
         // render all six faces at startup
         UpdateCubemap(63);
     }
 
     void LateUpdate() {
         if (oneFacePerFrame) {
             int faceToRender = Time.frameCount % 6;
             int faceMask = 1 << faceToRender;
             UpdateCubemap(faceMask);
         } else {
             UpdateCubemap(63); // all six faces
         }
     }
 
     void UpdateCubemap(int faceMask) {
         if (!cam) {
             go = new GameObject("CubemapCamera");
             go.AddComponent(typeof(Camera));
             go.hideFlags = HideFlags.HideAndDontSave;
             go.transform.position = transform.position;
             go.transform.rotation = Quaternion.identity;
             cam = go.camera;
             cam.farClipPlane = 100; // don't render very far into cubemap
             cam.enabled = false;
         }
 
         if (!rtex) {    
             rtex = new RenderTexture(cubemapSize, cubemapSize, 16);
             rtex.isCubemap = true;
             rtex.hideFlags = HideFlags.HideAndDontSave;
             renderer.sharedMaterial.SetTexture ("_Cube", rtex);
         }
 
         cam.transform.position = transform.position;
         cam.RenderToCubemap(rtex, faceMask);
     }
 
     void OnDisable() {
         DestroyImmediate (cam);
         DestroyImmediate (rtex);
     }
 }