This issue is addressed with ArcGIS 9.1 Service Pack 2 (SP2)
Performing route network analysis with the reordering stops option specified on a hierarchical network dataset results in a route with missing segments between stops.�When this occurs, the routes total cost and directions will be incorrect.
This is a known issue.
** This issue is addressed with ArcGIS 9.1 Service Pack 2 (SP2) **
Download the Service Pack from the link in Related Information section below.