Track as Asset Check box for Manual Invoices in R12

Dear Freinds

I was wondering if you might know the answer to the following question?

We’ve created a Non-PO invoice in the AP subledger then validated and Force approved the invoice.

Tracking the invoices through to Invoice Workbench the ‘track as asset’ field is not marked? How the system works for this flag for manual invoices in AP ??

I’m just wondering at which stage the system would recognise a Non-PO invoice as a potential asset, and also what prompts the system to recognise it as such? Or is it a manual process that the invoice needs to be marked ‘track as asset’ by a user?