Dear Steve, suppose you have a customer (and it seems you have) that wrote a code like "new ReferenceCacheEntryImpl(...)"
Also suppose that such code was compiled using 4.2.14 and deployed to production. Suppose that after several days server admin updated Hibernate jar from 4.2.14 to 4.2.15. Finally, suppose somebody calls ew ReferenceCacheEntryImpl(...) ... BOOM! Runtime error!