URL without /doc/lib shows results (incorrect page display)

As an example, here is a correct link:

https://www.boost.org/doc/libs/1_89_0/doc/html/stl_interfaces.html

which works, and matches

https://original.boost.org/doc/libs/1_89_0/doc/html/stl_interfaces.html

The boost.org website seems to also support an unexpected URL:

https://www.boost.org/1_89_0/doc/html/stl_interfaces.html

That page isn't online on original.boost.org. It's a new invention of website-v2.

1. Investigate the explanation, the git commit history, about why the unusual URLs are working this way. Was it intentional?

2. Most likely, these URL routes should be disabled. So search engines don't discover them, and advertise the wrong pages.