Some dozen years ago, I had a high end Bianchi with a threadless carbon steerer and a chorus group. I was going crazy because the headset would loosen with every ride. I torqued the clamp bolts to spec, and then tighter. Seems I was even messing with the bolt that went through the cap.
I finally figure out that it was because the nylon conical centering washer was not rigid enough to keep the steerer tube centered. The movement was forcing the stem up. I put in a Cane Creek headset with a metal centering washer and all was right with my world.
I would hope that Campy would have fixed the problem soon than later. I mentioned the problem to a shop mechanic once and just got a blank look. Have others had experience with this problem. It's a moot point for me at this point, but I am curious.