I know I've had this problem before. Not sure I recall the exact remedy for it, but here are a few things to check that might help:
Go to Tools -> AutoCorrect Options. Then click on the "AutoFortmat As You Type" tab. There, you can turn off the smart quotes, replacing -- hyphens with straight dashes (which might be a part of your problem). I *believe* your problem is most likely coming from "Border Lines" in the "Apply as you type" section. I know, for me, that turns my *** into a line of annoying blocks.
You'll also want to check things on the "AutoFormat" tab as well.
Hope this helps!
Sara