In stage 8-3, the slope you encounter in the second room in the Japanese version is a little glitchy. If the player decides to walk and subsequent crouch on the slope, this could possibly put you behind the slope into the out-of-bounds area. This slope happens to be the only occurrence in the game to do this. Crouch-sliding into a wall can make Kirby partially enter said wall. This glitch was fixed in the International version by making the slope completely solid so you couldn't interact into the out-of-bounds area.