Yes I saw that behavior before. That's probably because the you are persisting the session and the Environment keeps a reference to the old entity manager that has some value cached. When you reinitialize the environment to load once again the session you clean that object and the session is restored completely fromt the BD and works again without an inconsistent state.
If you think about the purpose of loading a session, is that you will load the session in a different thread where you need to initialize the environment once again. Cheers