When we have an object and we modify a field, before the UPDATE statement is issued it (correctly) calls jdoPreStore. In Our jdoPreStore we do a query to check for other objects of that type. The query just happens to return the same object, but it returns it with the dirty fields values replaced by the datastore values. This means that the fields are still marked as dirty in the object yet the changes are lost. The query should return the unique object, and only use the datastore values when those fields are not loaded (i.e preserve any dirty fields)