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For the present, I've found that the mark, which shows up in posts as a question mark inside a black diamond, can be corrected by clicking on "Preview" before submitting the post. In "Preview," you can delete these marks. If a quotation mark has been eliminated it can be replaced, in "Preview," with the quotation mark key on your keyboard. This editing process should eliminate all these question marks inside black diamonds. Double check by hitting "Preview" again. If all is okay, then hit "Submit."