Nested Coroutines: last coroutine quits early

Greetings,

I am trying to nest Coroutines. It seems to work OK, except that the last nested coroutine exits early.

In a nutshell, here's what I'm trying to do (in pseudocode)

 // start coroutine "add to scene"
 
    // start coroutine "fade to black", yield
 
    // does some simple logic
 
    // start coroutine "fade in from black", yield

As you can see, I want my "add to scene" Coroutine to be "wrapped" in the complete execution of two other Coroutines, fading a Unity.UI Panel in and out (using Color.Lerp and adjusting the alpha channel of the start color to determine the end color).

The first Coroutine "fade to black" works totally fine; it fades out as expected. Then, the simple logic is performed, as expected.

However, the final Coroutine "fade in from black" seems to yield only one time, even though I am using the same type of yield return statement on it.

What am I doing wrong here?

Here's some mildly redacted example code:

   private IEnumerator TransitionToScene(string sceneName) {
     Debug.Log("Transitioning. Starting fade out...");
 
     //Start a fade-out
     yield return StartCoroutine(Fade(FadeStyle.FadeOut));
 
     // OTHER STUFF IN HERE
 
     Debug.Log("Loaded! Fading in, now...");
 
     //Start a fade-in
     yield return StartCoroutine(Fade(FadeStyle.FadeIn));
 
     Debug.Log("Fade in complete");
   }

Here's the actual "Fade" Coroutine, also:

   //Create a Coroutine which will fade in or out
   private IEnumerator Fade( FadeStyle style, float fadeTime = .25f ) {
 
     //Early exit for invalid fade style
     if(style == FadeStyle.Invalid) { Debug.Log("INVALID FADE: Early-exit."); yield break; }
 
     Debug.Log("Fade coroutine started...");
 
     //Keep track of our fade progress out here for the coroutine...
     float fadeProgress = 0;
 
     //Grab the start color
     Color start = fadeImage.color;
     //Create a target color based on the start color...
     Color end = start;
     //If we're fading in, the target alpha is 0. If we're fading out, it's 1.
     end.a = style == FadeStyle.FadeIn ? 0 : 1;
 
     Debug.Log("Fading from " + start + " to " + end);
 
     //While we have not faded, yet...
     while(fadeProgress < fadeTime) {
 
       string inOrOut = style == FadeStyle.FadeIn ? "In" : "Out";
       Debug.Log("Fade " + inOrOut + ": " + fadeProgress  + " / " + fadeTime);
 
       //Calculate how far along we should be in the color transitions...
       float lerpVal = fadeProgress / fadeTime;
       Color newColor = Color.Lerp(start, end, lerpVal);
 
       //Apply it
       fadeImage.color = newColor;
 
       //Increment time
       fadeProgress += Time.deltaTime;
 
       //Continue next frame
       yield return null;
     }
 
     Debug.Log("Fade coroutine complete... (" + fadeProgress + " / " + fadeTime + ")");
   }

And, finally, some debug output:

 Fade coroutine started...
 UnityEngine.Debug:Log(Object)
 <Fade>c__Iterator0:MoveNext() (at Assets/SceneManager.cs:75)
 UnityEngine.MonoBehaviour:StartCoroutine(IEnumerator)
 <TransitionToScene>c__Iterator1:MoveNext() (at Assets/SceneManager.cs:160)
 
 
 Fading from RGBA(0.000, 0.000, 0.000, 0.998) to RGBA(0.000, 0.000, 0.000, 0.000)
 UnityEngine.Debug:Log(Object)
 <Fade>c__Iterator0:MoveNext() (at Assets/SceneManager.cs:87)
 UnityEngine.MonoBehaviour:StartCoroutine(IEnumerator)
 <TransitionToScene>c__Iterator1:MoveNext() (at Assets/SceneManager.cs:160)
 
 
 Fade In: 0 / 0.25
 UnityEngine.Debug:Log(Object)
 <Fade>c__Iterator0:MoveNext() (at Assets/SceneManager.cs:93)
 UnityEngine.MonoBehaviour:StartCoroutine(IEnumerator)
 <TransitionToScene>c__Iterator1:MoveNext() (at Assets/SceneManager.cs:160)
 
 
 Fade In: 0.001157403 / 0.25
 UnityEngine.Debug:Log(Object)
 <Fade>c__Iterator0:MoveNext() (at Assets/SceneManager.cs:93)
 
 
 Fade In: 0.008806617 / 0.25
 UnityEngine.Debug:Log(Object)
 <Fade>c__Iterator0:MoveNext() (at Assets/SceneManager.cs:93)
 
 
 Fade coroutine complete... (0.2785531 / 0.25)
 UnityEngine.Debug:Log(Object)
 <Fade>c__Iterator0:MoveNext() (at Assets/SceneManager.cs:109)