I actually think experiencing it first hand, when he met Itachi, has to do something with it. I mean, Kakashi is smart enough to have analyzed the way the mangekyou works. Plus, when they meet again in the manga, the way Kakashi speaks about MS makes Itachi suddenly worried. Remember, he said "Kakashi-san, you... you couldn't have, could you?".
Nice work on the banners.
