Why can't a MonoBehaviour subtype with generic arguments be serialized in a list since Unity 4.5?

Previous to unity 4.5 we could have serialized list fields of a type with generic arguments provided that the type derived from MonoBehaviour. This was a powerful abstraction technique which allowed us to avoid having to write concrete classes for every possible generic argument.

No one seems to be aware of this on the web and I am wondering what has happened. Is it deprecated functionality? If so does anyone know why and how to work around it without writing countless concrete classes? I have already sent a bug report in case it is a bug.

Here is an example of what I mean:

 public class GenericMonoBehaviourContainer : MonoBehaviour 
 {
     //this turns up in the inspector previous to Unity 4.5
     [SerializeField] private List<GenericMonoBehaviour<GameObject>> _behaviour;
     //this will turn up in the inspector regardless
     [SerializeField] private List<NonGenericMonoBehaviour> _concreteBehaviour;
 }
 
 public class GenericMonoBehaviour<T> : MonoBehaviour 
 {    
 }
 
 public class NonGenericMonoBehaviour : GenericMonoBehaviour<GameObject> 
 {
 }
 

Edit: I have just found out that previous to Unity 3.5 the serialization only works if the field is a list so I have updated the code example and question.