If a requested path (e.g. /music/offspring) does not have an exact representation in {menu_router}, but could be a subpath of another existing menu entry (e.g. /music), Drupal will currently not display a 404 but output the existing page with the remaining path as arguments (whether they are used or not).
I find this behavior both confusing to the user as well as SEO unfriendly, because it makes it possible to request the same content from multiple URLs. It's also an attack vector to page cache flooding related to: #1245482: URL variation DOS attack protection
If a new default behavior would break too many sites, there should at least be an option to switch between the two interpretation modes.
Keep in mind that, in any case, modules will always able to define wildcard URLs by explicitly including "%" into the path.
Comments
Comment #5
dawehnerNote: This feature was implemented in the D8 routing system.