This sounds like a relatively new Pinarello Vola carbon fibre fork. The crown of these forks is much deeper than normal, as are the rear brake bridges on Pinarello frames with carbon fibre stays. When you buy the frame/fork Pinarello normally supplies the longer brake nut/sleeves (at least they used to). If you have Pinarello frame with carbon fibre stays, you can probably mount the rear brake using the longer sleeve/nut intended for the front brake. You can buy longer sleeves/nuts for the front brake from a Pinarello dealer.