Post delete should be removing that post as the last post. Not sure why it's broken. I'll investigate.
The last issue was caused by me repeatedly editing that topic to be an announcement forum-wide because other issues were causing it to be stripped of its announcement status. Any time you post an announcement or reply to it, that post is listed as the newest post in that forum. That should go away now that I fixed the issues causing the announcement to break in the first place.