This has been an issue with almost every street car that can go over 300km/h, for a few months by now, it's not exclusive to the Veyron. All of my engine swapped cars exhibits the same behavior after said speed if I'm using tires of equal compounds on both axles.
Try using tires of inferior grip on the front, it's what I had to do fix my maxed cars, I'm running full wets on the front and racing softs on the rear. Also remove any toe angle.
Or crank up the front sway bar, add some camber, and fine tune the LSD, it seems to help with the issue as well.
But if you can't tune the car at all(if it's it's driving mission, for instance) then you're **** out if luck because there's nothing to be done.
I suspect this issue is something to do with the tire grip at higher speeds, but I can't confirm it.