Book outline not limited to allowed content types

This seems too obvious, but the book module's outline is not restricted by allowed content types on the node/add form.
To reproduce:
1) Standard profile installation 8.2.7 and enable the Book module.
2) Go to /admin/structure/book/settings and select only the "Article" content type for "Content types allowed in book outlines".
3) Go to /node/add/page to create a new "Basic Page". Notice, the "Book Outline" fieldset is visible although you'd expect the settings in #2 to restrict the Basic Page content type.