I have a Domain with two same-sized Leaderboards (728 x 90, Banners) and one Medium Rectangle (300 x 250, Block) on every Website. This answer says that
if you place more than one ad unit on a page, our [Google Adsense's] system will display unique ads to each ad unit.
Unfortunately the two same-sized Leaderboards often show exactly the same advert. Is this only related to personalized advertising or is this an issue of my code?