Oops. Even us that have been around here a bit double post. I even refreshed on the first one and rewrote it when I didn't see it. LOL....
The FR server has a cache to help faster loading when a lot of posters and lurkers are online at the same time.
That's why you will sometimes get double posts. When you post and the page is reloaded from the cache, your post won't show up right away. Thus, some people post again thinking that their comments weren't posted.
To prevent this, simply refresh your browser window several times after posting. Your post should then show up.
If it doesn't (it means FR is experiencing a lot of traffic), leave that window open, and open a new window on a different post. After you get through reading the new one, refresh the 1st one and your post will be there.