See user mailing list "HashCode corrupted on deserialzing map"

Currently Xstream always serializes subclasses before superclasses. For example:

public class Person {
  public String name; //getters and setters
}
public class Employee extends Person {
  public String address; //getters and setters
}
becomes serialized as:
<Employee>
  <address>street 15</street>
  <name>John Smith</name>
</Employee>

Besides the unlogical aesthetic aspect, this corrupts maps in subclasses that use keys based on superclassses (see user list).

The solution would be a boolean configuration property that enabled/disables superclass serializing before subclass serializing.
I would even propose to make enable it by default and provide disabling for backwards compability...