Don’t know the root cause is, but the end result comes from copying and pasting. Jim and John are working on it.
You can’t prevent it, but you can correct it by deleting or backspacing over any strange characters that you notice in the preview before you post, and replacing them by typing whatever they were — a double quote, apostrophe, or dash.
Okay ... that makes sense. It has to do with coding. This is one of the rare instances where I had to copy and paste the article because I could not find the developer code on the site. Most frustrating.
Doesn’t always work.