Open Stack

> If an object A contains another object or object list (called 
> sub-object), any change happened in the sub-object can't be detected 
> by obj_what_changed() in object A.

Well, like the Instance object does, you can override obj_what_changed()
to expose that fact to the caller. However, I think it might be good to
expand the base class to check, for any NovaObject fields, for the
obj_what_changed() of the child.

How does that sound?

--Dan