I believe it means the same thing so if it's not accepted, report it.
Theoretically, uninteresting would corresponds to «неинтересно». :D However, I'm not sure this distinction makes any sense.
The distinction makes sense. Мне не интересно, а скучно. Это неинтересно.
Yeah, I know that rule. But does this rule reflect the inherent difference in the language, or is it just an orthographic rule? I personally don't know.