During XML Import, a child of a non-Model will cause import to break

(Bug, Investigate , Priority: High, Test Status: No automated tests yet , Reported By Justin du Coeur, )
Import and Export
Summary: This is hard to set up nowadays, but if you manage to have a child Instance of an Instance (not a Model), the resulting XML winds up confused. The parent Instance gets used as a Model node, without a matching Model record, and the Importer goes boom.
Found this by accident in the A Respectful Calm Space.