For more clarity, do a diff between the start() functions of
net.sf.ehcache.hibernate.EhCacheRegionFactory
vs
org.hibernate.cache.ehcache.EhCacheRegionFactory

The missing functionality is
manager = new CacheManager(HibernateUtil.overwriteCacheManagerIfConfigured(configuration, properties));

This is useful in letting our users create multiple cache managers without creating an absolute cacheconfig xml.
Just a different cache manager name would suffice.