Yes - I've noticed that too, as well as with ellipses (...), and I think it's because Microsoft Word does something with the formatting of those. Like when you make an ellipse, it doesn't leave it as three periods; it formats the dots so they are closer together or something so it's like one punctuation mark instead of three separate ones. And apparently AC doesn't like that! The other place I've noticed it in my stories is between sentences, and I bet it has something to do with the fact that I use two spaces instead of one between sentences. I know you don't have to use two spaces between sentences anymore, but I was taught to type the traditional way, and it's a habit I can't seem to break (plus, I think it's easier on the eyes to have two spaces between sentences). I'm not sure why that is suddenly causing a problem for AC, but it does.
Ever since I moved my site to Wordpress, I have started copying my chapters from there instead of Word to paste into AC when I go to update because they already have the HTML formatting that way, whereas when I used to copy/paste directly from Word, I would have to add in all the formatting myself to center text or make it bold or italicized, etc. But those are the chapters that now suddenly have these symbols all over the place, whereas my older stuff does not. I'm not sure why that would make a difference - I actually thought it would be better to get rid of the weird formatting stuff that Word sometimes does - but yikes, I guess I'll have to go back to my old way of posting.