MVC should know about entities lying in the session
If you want to prepare/edit/create an entity over some steps before you want persist it in the database, you will put it somewhere in the session. So far so good. As soon as you have an entity lying in the session and want to forward or redirect it to another action the persistence manager will be asked to return the identifier, to encode and decode the object to/from its identity array. As the entity is not yet added to a repository, the persistence manager will return FALSE and the forward/redirect breakes.
We should enable the persistence manager to know about every entity in the session and look at them before asking the underlying persistence layer (e.g. doctrine).