I got update to work with a single IMG tag. When I went back and tried with real posts have been unable to get update to finish. Tried 3 computers (Win 8 and XP) on my home network and all fail to update post with IMG tags. Also tried from remote connection to server running with a different ISP. That update fails too.
Perhaps you can find something in your logs to indicate the failure, nothing displays on my end.
The Firefox Network log from my last attempt a few minutes ago shows
POST 23706928 with a status code of 302 Found
Get error with status code 404 Not found for http://www.avsforum.com/error
First noticed problem yesterday and after several attempts submitted error report.