Where is the cracking? If it is at the edge of the panel it is caused by the panel shrinking inside the "frame" of the rails and styles of the door. Raised panel doors are a very old fashioned way of holding a panel within a frame. Since there is a large piece of wood (the panel) there is an allowance for it to expand and contract (contract in the winter when the air is dry and expand in the humid summer). The edge of the panel "floats" in grooves cut into the surrounding door frame (called styles and rails). If you paint the panel in the summer when it is expanded then there is a chance that when it contracts in the fall/winter that it will crack the paint at its edge. It may even end up showing some bare wood near its edge. If you glued the panel to the frame, or the paint acted as glue, then there is a chance that the panel itself will crack while trying to shrink. This is pretty rare. You probably have cracks on the edge of the panel. Wait until February, scrape and sand at the cracks and repaint. With any luck, it won't look too bad when the panels swell and shrink in their next seasonal cycle.