This seems to happen in 4.2 branch at EntityEntryContext#reentrantSafeEntityEntries (https://github.com/hibernate/hibernate-orm/blob/4.2/hibernate-core/src/main/java/org/hibernate/engine/internal/EntityEntryContext.java#L211). I'm pointing out the 4.2 code here because it's the most recent affected release.

The following:

managedEntity = managedEntity.$$_hibernate_getNextManagedEntity();

is returning a non-null value when processing what Hibernate expects to be the last managedEntity.

Somehow the count field is not consistent with the actual contents. I'm not sure how this got out of sync.