Welcome to the Forum. The only thing I can think of re: inappropriate pooping is, kitty feels like the litter box isn't clean enough? Some cats are very picky. Would need to know more details but for a single-cat home, the LitterMaid automatic litter boxes are really nice for keeping the box clean between uses.
"I love cats because I enjoy my home and, little by little, they become its visible soul."--Jean Cocteau