Dear Steve, I am very happy that I'm chating with such cheerful and experienced man! While I typed the previous sentence, I came twice. The only thing I'm afraid of - you may say that this is not enough respect.

According to [1], the original class was created in Dec 2012, and ReferenceCacheEntryImpl constructor has been changed in Jul 2014.
According to [2] this fix has been backported in 4.3.6 and 4.2.15.

It means that ReferenceCacheEntryImpl(Object, String) existed for about 18 month, and after these months it was replaced by ReferenceCacheEntryImpl(Object, EntityPersister) [1].

I don't know how compatibility risk management works in Hibernate and I'm not sure many people was really affected by this change.
My idea is just to draw your attention to the fact that you public API has this particular incompatibility.

[1] https://github.com/hibernate/hibernate-orm/commits/master/hibernate-core/src/main/java/org/hibernate/cache/spi/entry/ReferenceCacheEntryImpl.java
[2] https://hibernate.atlassian.net/browse/HHH-9269

P.S.: It would be very cool if you show me any document with the rules about how we may change Hibernate API from one (major, minor) version to another (major, minor) version.