Here’s what just happened to me.
I closed and restarted Scrivener to refresh images, and I was entering some text into a post in this forum. As I started typing the word “missing,” Scrivener finished loading, and grabbed focus from my browser.
As a result the letters “mi” did not go into my post, but were intercepted by Scrivener. Whether they were entered into the text somewhere I don’t know. I wouldn’t want to have my book published and find a random “mi” in there.
I don’t know where those letters went, but S shouldn’t grab focus.