Which purchasing org is being used in SC creation - local or backend?

Hi guys.

SRM 4.0, server 5.0, ECS.

When creating the SC in SRM, the local purchasing organization from PPOMA (flagged as pur org but with no backend specifications) is used - how does this local pur org get changed to the corresponding backend purchasing organization (flagged as pur org with backend specified in PPOMA)?

My org structure:

ROOT:

Company 1 (flagged as company)

> LOCAL purchasing org (flagged as pur org, but no backend)

> LOCAL purchasing group (flagged as pur grp but no backend)

> Users

> Approvers

> BACKEND purchasing org (flagged as pur org, and backend plus backend org specified)

> BACKEND purchasing group (flagged as pur grp plus backend plus backend pur grp specified)

Again: When creating the SC, the LOCAL pur org is being used, so how is this being determined to belong to the BACKEND purchasing org unit? I am having issues where several different purchasing orgs and groups are responsible for each other, and it seems to be rather coincidential which pur org is used - I would suppose that when the LOCAL is used, the corresponding BACKEND will be chosen.

DM