Errors using StopCoroutine with nested coroutines

I am having trouble stopping nested coroutines using StopCoroutine. I included minimal code for a component (CoroutineTest) that reproduces the issue at the bottom of the question.

If I Play a scene in Unity with a CoroutineTest component attached and active to a game object, and then Stop the game a second later, I get the following errors while the game is trying to quit:

 coroutine->m_WaitingFor->m_ContinueWhenFinished == coroutine
 coroutine->m_RefCount > 0
 coroutine->m_CoroutineEnumeratorGCHandle != 0

All with the same callstack:

 UnityEngine.MonoBehaviour:StopCoroutine(Coroutine)
 CoroutineTest:OnDisable() (at Assets/CoroutineTest.cs:15)

The errors are a little vague but it looks like they some kind of garbage collection failure with my coroutines. I'm not sure what I'm doing wrong.

I noticed two things:

1. I get no errors if I use StopAllCoroutines instead of StopCoroutine(outerRoutine)

2. I get no errors if I no longer nest a call to StartCoroutine(InnerRoutine())

I would like to keep some coroutines running when the component is disabled, while stopping others, so StopAllCoroutines is not suitable for me. Is there a way I can use StopCoroutine without causing errors when the game stops?

Here is the code for the component:

 using System.Collections;
 using UnityEngine;

 public class CoroutineTest : MonoBehaviour
 {
     private Coroutine outerRoutine;

     public void OnEnable()
     {
         outerRoutine = StartCoroutine(OuterRoutine());
     }

     public void OnDisable()
     {
         StopCoroutine(outerRoutine);
     }

     private IEnumerator OuterRoutine()
     {
         yield return StartCoroutine(InnerRoutine());
     }

     private IEnumerator InnerRoutine()
     {
         yield return new WaitForSeconds(4f);
     }
 }