Why would you be painting over the prefinished stuff? If you're talking about an exposed side piece, It should have an unfinished skin on it. YOu should only paint the frame, and any exposed sides.Thanks.
Any adhesion problems painting over the finish (for the exteriors)?
Its been a while since I've built any cabinets, but I believe the prefinish is only on one side of the plywood anyway. For cabinets with two sides of shelves, there would be two plywood pieces in the middle to hold the shelves.