I've had those for a couple months now. I also have them for the regular block units as well, they convert much better because they look less like an AD.
I always thought it was an Internet Explorer browser issue/bug. My 728x90 leaderboard has been showing that way (horizontally) for a while now, but ONLY in Internet Explorer. However, I just checked my site now in Internet Exploerer... and the leaderboard is now showing ads vertically.
Right now, I could see the normal Ads not the premium ads. Anyway the guy is lucky to have them on his website.
Thanks, if you can see them again, remember to capture and share as I need to see that in vertical format too