Cannot add Agreement to Manual PO

Summary:

When creating a manual Purchase Order and trying to add a Purchase Agreement to the Line, no values are returned under Source Agreement section

Content (please ensure you mask any confidential information):

Am I going crazy or there's a bug here?

1. Create and approve Purchase Agreement.
2. Create a manual Purchase Order (no PR).
3. Search for the Agreement at Line level, but no results are returned.

Screenshots below:

There is an note on support, BPA In Source Agreement Field On PO Line (Doc ID 2594492.1), that does not provide a clear answer - it insinuates that you cannot link a manually created PO to an Agreement?!