Wordpress sometimes "guesses" a redirection for a nonexistent page slug if the slug is at the contained in another URL. After some searching, my hypothesis is that this part of the canonical redirection functionality, which can be disabled using this code:

remove_filter('template_redirect', 'redirect_canonical'); 

However, I like the idea of canonical redirection, and would prefer not to turn it off entirely. Is there a way to only disable the slug "guessing"? I would prefer a 404 over an incorrect 301.