Disable ONLY URL auto complete, not the whole canonical URL system
Updated Answer (2020-10-29): The solution has changed with WordPress 5.5. Keeping the old answer for reference below. Short version: Get my pluign from here: https://wordpress.org/plugins/disable-url-autocorrect-guessing/ Long Version: With WordPress 5.5, you can control more precisely if/how the guessing should work. Refer to https://make.wordpress.org/core/2020/06/26/wordpress-5-5-better-fine-grained-control-of-redirect_guess_404_permalink/ for more information. To completely disable guessing, use this code: add_filter( ‘do_redirect_guess_404_permalink’, … Read more