I'm not sure if this is iOS 8 related or just iOS related but it seems to be worse on iOS 8. My iPhone is constantly correcting legit words into something else. It always change "on" to "in". It changes "not" to "nit" These are just two examples but it is doing this all day, every day. Sometimes it changes to words that aren't even real words. Other times it changes real words to other real words. I'm constantly trying to re-teach it but it doesn't seem to take.