I'm having all sorts of oddities with Sierra. It was true before the latest update. Not fixed. Pages was also behaving strangely, with text disappearing as I typed, then reappearing.
Anyone else seeing this kind of stuff. Very annoying. Also very unusual for a Mac OS. I've never seen this kind of thing in the past.
It seems to happen when I wake my machine up. If I log out and log back in, it seems to fix it. At least that's how it looks at this point.