Re: Sense 6 word guessing
In my case that only happens when I'm tweeting with Plume. With the official Twitter app I haven't seen it do that but I don't use the official app too often.
In WhatsApp or the stock SMS app I don't see that behavior. If you are using a third party texting app try using the stock one and see if the happens with it.
It is either a bug or (if only on certain apps) a bad implementation from the app that affects Sense word prediction or keyboard in general. I remember some apps, Plume among them, had not too long ago an option/workaround to allow for auto correction on Sense keyboard.