[sqlalchemy] polymorphic inheritance where an engineer is also a manager

Michael, et al: The excellent documentation uses the example of an Employee from which Manager and Engineer inherit. What to do when an Manger is also an Engineer? My thought is that I want some kind of Adjacency relationship as

[sqlalchemy] sqlalchemy.orm.exc.StaleDataError upon migration from SQLAlchemy 1.1.15 to 1.2.0 or 1.2.1

Gnu Mailman 3 uses SQL Alchemy to access SQL databases. We have an issue with one of or unit tests which passes with SQLAlchemy <= 1.1.15 but which fails with SQLAlchemy >= 1.2. The failure is independent of the backend (sglite, mysql or pgsql). Here's a traceback from the failure. Traceback