The KitchenAid bowl and base plate are designed to tighten in the same direction as the rotating beater so the bowl will not come out of the plate during mixing or kneading. Therefore, when kneading heavy dough, the bowl may be more difficult to remove.
The bowl can be loosened from the base plate by several sharp slaps on the sides of the bowl, using the flat palm of the hands in a rotating motion. If you still have difficulty loosening the bowl from the base plate, try putting a small amount of vegetable oil on a cotton ball and lubricating the base.