Apple has some tricks up its sleeve when it comes to the iPad keyboard in iOS 5. The addition of the split keyboard was helpful for people who enjoy typing with two hands while holding the iPad vertically. In this manner thumbs can more easily be used much like on the iPhone.
Now Finer Things in iOS has pointed out that there are actually hidden keys when typing in this mode. The keys found on the inside edge of the split keyboard are repeated on the opposite side, even though there's no key depicted.