This sounds the same one of our kittens, she will use the litter box fine but when she is up stairs she will just wee and poo in my room, apparently, when they can smell they have been somewhere once they will keep going there until the scent is gone. White vinegar is great for on the carpet where they have weed/pood and make sure u wash ur bed clothes in biological washing powder to completely rid the smell so then the kitten shouldnt go there again. Hope this helps :)