Soft 404 on SMF

[marcusslavorum]

If you click this non-existant link http://www.simplemachines.org/?-p4 it will redirect you to smf homepage. Same things happens on my website, i used to have a blog in root domain, so now those links are deleted but when someone goes to www.mydomain.com/ [nofollow]? -452 whatever link, it will give him a soft 404 and redirect him to home page.

Anyone know how to prevent this? i see the question mark for dynamic url creates the problem somehow.