Using the 'back arrow' immediately after submitting your post and before it has appeared on the forum will lead to double posts, and possibly before exiting that thread if you choose to check your posting, as I eventually worked out having got caught out several times
I just wait for the post to appear on the thread and then click on 'view unread posts' (or anything else on the site) which advoids the double posting................which so far has avoided the double posting problem