I think I know why it has happened to me. Safari sometimes hiccups and doesn't display the web page I asked for (or not within a reasonable time). It seems to turns a click into a NOOP. Usually this is harmless. If you click again, the web page usually appears.
Sometimes this happens when I click the "Post" button. Then, when I click again, the Post happens. Unfortunately, sometimes (always?) the Post has already happened with the first click. Since I didn't get the feedback, I automatically clicked again and posted again. To prevent this, I'll try checking the forum in another window to see if the post occurred.
Re: Duplicate Posts
Hope you know I wasn’t calling anyone out on it. I just seems to be noticing a lot more duplicates on FR recently than in the past. Thought maybe it was a known bug that had been discussed elsewhere on the site. Thanks for the reply.