When performing network traces that utilize weights, the trace results are inconsistent with the values of the weight field in the features. This happens only when those fields are foreign keys in relationship classes.
When you use the attributes inspector in ArcMap or IRelationshipClass to create and delete relationships, the embedded foreign key in the destination class is modified in such a way that the logical network is not messaged. Since the logical network is not messaged, the weight value from the field is not updated in the logical network.
If you manually modify the embedded foreign key, by explicitly changing its value using the attributes dialog, the logical network is messaged.
You should not used embedded foreign keys as network weight fields.