Adding to this just to say that this is still a problem, I was quite thrown off when trying to view the colouring contest winner's pages only to be redirected to my own page! Rather than being directed to the page with the user's ID, we're being linked to the page of their USERNAME, which is an invalid format and defaults to our own profile.
While it's not good in any case, I find it is particularly unfair to the winners that I can't easily view their profiles and for example, request to be added to CA pinglists if they might have any- without using forum search features. It's an extra step that might cause them to lose out on publicity- and generally feels like a small but important feature to fix.