What are the keys you use to create an em-dash?
You know, a long em-dash? I read that there's a combo of keys you press here, but I can't find that post/thread.
Em dash for Word (—): Alt+0151
And you can almost guarantee it will be changed back to a double hyphen at the first edit. If you are using FD10 contact support and see how to set it up as an auto/option.