I already know how to work around it, but why is the URL stored in the database at all? Not once, but at least twice! (wp_options.siteurl and wp_options.home)
I understand some users might rely on this to use their site in a subdirectory, but I'd guess they are the "fringe" users, and the default behavior should not cater to them.
Many users are frustrated and confused by this, and it's a pain for administrators of multiple WP sites.
If I need to submit a patch, I'll make one, but I don't want to waste my time on it if it's just going to be brushed off because a core developer likes this irritating quirk.