Custom Key Results in ClassCastException in CacheLoader

If a a JCache is created using a read-through javax.cache.integration.CacheLoader using a custom Serializable key (in this case acme.MyCache$MyKey) a ClassCastException is thrown when trying to pass the key value of org.infinispan.marshall.core.MarshalledValue instead of MarshalledValue#get() into the CacheLoader instance.

java.lang.ClassCastException: org.infinispan.marshall.core.MarshalledValue cannot be cast to acme.MyCache$MyKey
	at acme.MyCache$2.load(MyCache.java:1) [my-app-1.0.0-SNAPSHOT.jar:]
	at org.infinispan.jcache.embedded.JCacheLoaderAdapter.loadKey(JCacheLoaderAdapter.java:65) [infinispan-jcache-8.0.1.Final.jar:8.0.1.Final]