Determine update source for BSEG-ZUONR, FI Assignment field

Dear All.

How is bseg-zuonr, the assignment field getting updated?

We have an issue with Production Order settlement, transaction KO88, where the sales order and line item is being updated to the assignment field (bseg-zuonr) rather than the production order.

Normally this works fine, the sort field determines the aufnr and updates the assignment field with the production order.

In this case though, the process is MTO(make-to-order) so the sales order generates a production order. Somehow the program overrides the config and passes the sales order and sales order item number that generated the production order to the assignment field.

So, I'd like to see where bseg-zuonr is getting updated in this process. I checked "SAPLKO71", the program behind KO88 but didnt' find anything.

I might be able to single step all the way through, but not sure how effective that would be and looks to take a long time.

Does anyone know how to determine where in the code this is occuring?

Many Thanks!