Bert, in an ideal world, it shouldn't happen. It's a problem that afflicts many cars - my XKR used to do it, DB7's do it and I think some DB9's too. The Vanquish had air con in the actual headlamps to cure it.
I've put the question to my Aston guy to see if there's a solution.
It will be of little comfort to you to know that I was able to forget about the problem in the XKR - sometimes they were fogged, somedays they were not. However the XKR was a daily driver and not the precious thing that the GT is.
I'll see what the Aston people come back with and report back. Maybe some of the well connected people here could ask Ford....
Neil