Fade in / Fade out material goes to 100% opacity for a fraction of a second

Hi I'm using the following script to fade between level loads on GVR. The fades work fine when triggered manually but if they are triggered by a button click calling "FadeOut()" the material goes to 100% opacity for a fraction of a second then fades as expected from 0 - 100.

I'm stuck so any help is appreciated...

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3. using UnityEngine.UI;
4. using UnityEngine.SceneManagement;
5.  
6. public class ScreenFaderSphere : MonoBehaviour {
7.  
8.     public bool fadeInOnStart = true;
9.     public float fadeTime = 2.0f;
10.     public Material faderMaterial;
11.    
12.     public Color fadeColor = new Color(0.01f, 0.01f, 0.01f, 1.0f);
13.     private bool isFading = false;
14.     public string nextSceneName = null;
15.    
16.     void Awake()
17.     {
18.         if (faderMaterial==null) Debug.LogError("fader material not found");
19.     }
20.    
21.     void OnEnable()
22.     {
23.         if (fadeInOnStart) StartCoroutine(FadeInRoutine());
24.     }
25.    
26.     void OnLevelWasLoaded(int level)
27.     {
28.         if (fadeInOnStart) StartCoroutine(FadeInRoutine());
29.     }
30.    
31.     public void FadeIn()
32.     {
33.         StartCoroutine(FadeInRoutine());
34.     }
35.    
36.    
37.     IEnumerator FadeInRoutine()
38.     {
39.         float elapsedTime = 0.0f;
40.         faderMaterial.color = fadeColor;
41.         Color color = fadeColor;
42.         isFading = true;
43.         while (elapsedTime < fadeTime)
44.         {
45.             yield return null;
46.             elapsedTime += Time.deltaTime;
47.             color.a = 1.0f - Mathf.Clamp01(elapsedTime / fadeTime);
48.             faderMaterial.color = color;
49.         }
50.         isFading = false;
51.     }
52.  
53.  
54.    
55.     public void FadeOut()
56.     {
57.         StartCoroutine(FadeOutRoutine());
58.     }
59.    
60.     IEnumerator FadeOutRoutine()
61.     {
62.         float elapsedTime = 0.0f;
63.         faderMaterial.color = fadeColor;
64.         Color color = fadeColor;
65.         isFading = true;
66.         while (elapsedTime < fadeTime)
67.         {
68.             yield return null;
69.             elapsedTime += Time.deltaTime;
70.             color.a = Mathf.Clamp01(elapsedTime / fadeTime);
71.             faderMaterial.color = color;
72.         }
73.         isFading = false;
74.         if(!string.IsNullOrEmpty(nextSceneName))
75.             SceneManager.LoadScene(nextSceneName);
76.     }  
77.  
78. }