How does WordPress redirect mistyped URLs to the correct one?

Well, I’m not sure exactly because it is A LOT of code, but to make it stop, you can use the filter ‘redirect_canonical’ and return false.  like so:

add_filter( 'redirect_canonical', '__return_false');

So say you have a post named “mission” at http://mydomain.com/mission, but for some reason you really want to go to http://mydomain.com/mission-control/ instead of being redirected to the post, returning false with redirect_canonical will allow you to visit the url you want.

‘redirect_canonical’ is actually an SEO feature built into WordPress.  This function redirects duplicate content like www.mydomain.com to mydomain.com among other things.  Disable it with caution.