rawalex: I find it difficult to believe that somebody would not know how to clear their browser's cookies. It's a basic operation and there's detailed instructions online in many places:
The documentation covers it as the very first step in solving this problem:
And quite frankly, if telling somebody "clear your browser cookies" is not clear enough for them, then they should not be running their own website to start with. If they want a blog, but can't run a browser (much less a website), then they should farm it out to some other administrative system like http://wordpress.com , to let somebody else handle the actual work and to let them just post on their blog.
Now, the issue ck is seeing is what I'm trying to work out. However, it has little to do with the cookies if his definitions are getting set incorrectly. It would have more to do with his database or settings in the database.