Placing objects on a railroad

Two situations: 1) Placing a trap on a rail. The dwarf rides a cart that stops at the space of the given order. The order is denied, the order icon becomes red. 2) Placing a cart on a rail. The dwarf rides a cart that also stops at the space of the given order. The order is not denied, but now two carts occupy the same block. One cart will bug. Possible solution: make carts always stop one block before any given order.