I've turned notifications off for now as they seem to be the culprit for double posts, and I can't remember how I fixed the issue last time.
I'd rather have notifications back and the double post message (which I can choose to ignore), rather than no double post message but no notifications.
I'd rather have notifications too.
The double post problem is easily avoided by not hitting the original post when it reappears but just hitting "new posts" at the top of the screen