fault exception

Ok... at long last, I've a few things to report on the exception
resolving fault issue I first mentioned back in May.
Here's the brief:
Tables:
Assignment
    id: pk
    transactions: toMany to AssignmentTransactions
    parameters: toOne to AssignmentParameters
    type: used for inheritance
    unimportant attributes
AssignmentTransaction:
    id: pk
    assignment: toOne to Assignment (uses assignmentid FK)
    unimportant attributes
AssignmentParameters:
    id: pk
    assignment: toOne to Assignment (uses assignmentid FK)
    unimportant attributes

Objects:
Assignment (type is NULL)
AssignmentTransaction
AssignmentParameters
Exam (extends Assignment; type is "exam").

In the test case, which I will attach to a JIRA issue I will open, I
fetch an Exam from the database, create a transaction, and set the
transaction's assignment to be the fetched exam.  Then I refetch the
Exam from the database and try to access the parameters of the Exam, and
get the fault exception.  Specifically, the AssignmentParameters can't