`(set-on-new-window :path :default)` does not set a default route handler

[bitspook]

Documentation says:

If PATH is set to :default any path without another route and there is no static file matching the requested path ON-NEW-WINDOW-HANDLER and BOOT-FILE will be used

I understand this means in tutorial-12, all invalid URLs (e.g http://127.0.0.1:8080/blabla) should invoke on-default. But that does not happen, instead a blank 404 response is returned.

Can you please clarify if I am misunderstanding the expected behavior here, or if this is indeed a bug?