With the most recent version of the iOS, Apple decided to hide or make invisible 6 keys in addition to the ones existing in the split keyboard. The feature came as a result of the numerous requests received from the iPad users and while others did not know about it, they have probably noticed it while typing on the iPad keyboard.
If you use your iPad in portrait mode you will be able to type on the keyboard using your two thumbs, while also holding the iPad. This can be done because in iOS 5, Apple decided to split the keyboard in two parts, one on the right side of the screen and one on the left. This made typing on the iPad a lot more easier and comfortable if you do not want to switch to the landscape mode.
The Apple iPad user base loved the new split keyboard from iOS 5 but they also liked another feature. Apple decided to add 6 invisible or hidden keys, three on each side and one for each row which is basically the first key from the other side and row. With the 6 keys hidden by Apple you are able to type with your thumbs a lot faster.
Depending on the individual, some use a different type pattern that could sometimes lead to an uncomfortable position while typing, touching the wrong keys.
As an example, those of you who are left handed would feel the need to use the left thumb to tap on the Y key. Given the way that Apple imagined the split keyboard, this would not be possible so they decided to hide or make invisible six keys, one for each row.
This means that you will be able to use your left thumb to type the letter Y even though this key is on the right side of the keyboard. You would have to go to the opposite screen side or to accommodate with the right thumb for that letter. The same applies for the T letter, or right handed users for that matter.
When users touched involuntarily the screen next to the Y or T letters they noticed that the corresponding character had appeared on the screen. This made users thinking that the situation could apply for the G, H, B and V keys so this is how the six hidden and invisible keys were discovered.
You might not give that much importance to this feature but I’m pretty sure that you’ve accidentally typed the empty space next to the Y or T key. It is very likely also that you did not notice the keys being typed even though it was on the other side of the screen.
If you don’t know how to split the keyboard in iOS 5 yet, you can use two methods. The first one would be to pull apart the keyboard right from the middle while the second method would be to tap on the toggle keyboard button.