Audio Audio occasionally doesn't fade in/out properly

Hello all,
I'm currently trying to fade between sound clips using two audio sources and coroutines, but about 1% of the time the coroutine does not seem to run and leaves the music in its current state. Currently I am using a static AudioController class:

Code (CSharp):

1. public static class AudioController
2. {
3.     public static IEnumerator FadeOut(AudioSource audioSource, float FadeTime)
4.     {
5.         float startVolume = audioSource.volume;
6.         while (audioSource.volume > 0)
7.         {
8.             audioSource.volume -= startVolume * Time.deltaTime / FadeTime;
9.             yield return null;
10.         }
11.         audioSource.Stop();
12.     }
13.     public static IEnumerator FadeIn(AudioSource audioSource, float FadeTime)
14.     {
15.         audioSource.Play();
16.         audioSource.volume = 0f;
17.         while (audioSource.volume < 1)
18.         {
19.             audioSource.volume += Time.deltaTime / FadeTime;
20.             yield return null;
21.         }
22.     }
23. }

and I am fading between them by calling the following code:

Code (CSharp):

1. StartCoroutine(AudioController.FadeIn(musicSource2, 0.12f));
2. StartCoroutine(AudioController.FadeOut(musicSource, 0.12f));

I've attempted to recreate the bug but it appears very infrequently and I cannot seem to find any pattern. Does anyone have any ideas why this might be occurring (or know of a better way to fade between audio sources)?