This is one of those glitches that many iPhone 5 users may never encounter. But if you do, it's good to know that it's a known issue. An iOS developer was the first to notice that if you scroll diagonally by rapidly swiping back and forth on an iPhone 5, the display seems to freeze momentarily. After the developer posted about it online, Recombu, a product-comparison site, was able to replicate the glitch. They've posted a video demonstrating what happens. The video shows two iPhone 4S models side by side with two iPhone 5s. Making the same gesture on all devices, the 4S models handle it with no problem, but the iPhone 5s struggle with the challenge. One stopped reacting to touches and the other would stop responding momentarily and then start again.
While it doesn't seem to be a major problem, since there aren't many instances in which one would do that kind of scrolling, it could indeed impact the performance of some games, such as Fruit Ninja, which uses this kind of gesture.
Read more on the Recombu website.