That's exactly what happened to me when I drove the coupe at a factory open day. The only unfortunate thing was that I had Steve Morris sitting next to me. He was very good about it...he just said "we've only got one of these"!
I have to say the road was just as you describe weatherwise. I then took out the plus 8 (with a different member of staff) and that stayed in a straight line!
Great fun cars eh?
Nick