For some iOS’ old users, lowercase and uppercase letters problem in iOS sometimes really annoying. Since the words you type can be different with the keyboard, you type in lowercase but it shown in uppercase on your keyboard.
Usually we can use shift key to solve this problem. Apple has notice how the keyboard letters stay capitalized except the shift key being ON or OFF (left/right). This condition makes apple do some improvements in iOS9.
In iOS9 shift key not only capitalize the letters in the messages, but also on the keyboard. But for some old users that have been typing the standard way for so long, using the shift is kind of habitual that is hard to change.
If you want to go back to the non-changing keyboard try these steps. Go to Settings -> Accessibility -> Keyboard -> and slide off Show Lower Case Keys.
This can be enabled or disabled anytime, go to Settings -> Accessibility -> Keyboard. Happy cause apple doesn’t forget the old users that have some unchanging habitual, right?