JAV2I12 — Stream format problem for custom marshalled RMI types

There is a problem in the stream format for custom marshalled RMI types.
The Java serialization spec requires that when a class with a writeObject
method calls defaultWriteObject and then writes optional data, the receiver
must be able to skip the optional data if the readObject does not consume
it or the class is not in the receiver's hierarchy. So if the sender's
hierarchy consists of serializable classes Base and Derived, both of which
call defaultWriteObject and then write optional data, there must be a way
for the unmarshaller to first skip to the end of the Base data, then skip
to the end of the Derived data. With the current stream format, this is
not possible.

see below