I figured a different behaviour in Envers 5.0 compared to previous versions. It is related to the 2 settings 'RevisionOnCollectionChange' and 'GlobalWithModifiedFlag'. If both settings are set to true and the reference of one entity is changed, it ends up in an exception:
NHibernate.LazyInitializationException : Initializing[Envers5Bug.Person#1]-failed to lazily initialize a collection of role: Envers5Bug.Person.Cars, no session or session was closed
Since it is much harder to describe I prepared a very simple project which is revealing the problem. Please run Program.cs or Test.cs.