In previous versions of hibernate upto and including 4.2.8 the classpath order was respected when loading persistence.xml. The implementation was in org.hibernate.service.classloading.internal.ClassLoaderServiceImpl.getResources(String) which was implemented using an ArrayList

But since 4.3.0 the functionality appears to have been moved to:
org.hibernate.boot.registry.classloading.internal.ClassLoaderServiceImpl.getResources(String) using a HashSet introducing an undesirable random element into the ordering.