Interunit client - Interunit Expense inheriting fields ....why?

Below are the details of the issue:

1. the client is set up as an interunit client because we do not want AR items to post
2. we feed time transactions from an outside source into Project Costing
3. Projects are linked to a contract with a rate set
4. Contract is set up as an INTERNAL contract because the client is set up as interunit
5. interunit billing accounting entries are being created and the IE record is inheriting the anchor PC BU, project ID and activity ID
6. none of the inheritance rules include these fields
7. the journal entries are kicking because the information is not valid on the 'to' BU