Purchase Requisition - Combine Budget Nominal code following through

A client has setup Combine budgets and wants the relevant nominal code within to be default all the way through the PO process.

For example: Combine Budgets for 5000/Yr1, 5001/Yr1 and 5002/Yr1

Requisition raised against nominal 5000/Yr1 for free text time (does not use stock)

When in Generate PO section the correct nominal is there but once supplier is selected it defaults to supplier nominal code (5000). It should retain the nominal code from the combined budget 5000/Yr1.

Customer currently has to reenter this.