When I tried to register contest 1802 a div.2 contest which will take place along with a div.1 contest. Then codeforces told me "Rating should be between 0 and 1,899 in order to register for the contest". But actually users whose rating are below 0 also can participate in div.2, so it should be "below 1900" or something like that.

I know this isn't a problen at all, but it's just very interesting.