Instantiating packages from other repositories

Consider a MDR installation with two repositories "A" and "B". Currently 
it isn't possible to instantiate a package from repository A to create 
an extent in repository B. Is this restriction by design? Or, in other 
words, must the model, its metamodel, its meta-metamodel, etc., etc. all 
be in the same repository? Or, should it be considered a bug if this 
cross-repository instantiation does not work?

If this is the way it is supposed to work, then perhaps this condition 
should be documented. We could check for this condition in 
createExtent() and throw a CreationFailedException if this rule is 
violated. Currently, a non-obvious NullPointerException is thrown from 
inside MDRClassLoader, and maybe other places.

- Brian