Consider a setup with guests allowed to create threads and/or post replies, and all their messages have to be approved (permission Follow message moderation rules is set to Default/Deny for guests' usergroup). Guests can create threads and post new messages, but after doing this they are redirected to their thread or message and the url is something like /threads/title.id/ or /posts/id/ accordingly. The problem is that when guests redirected to that pages after posting a reply or creating a thread, they get standard permission error message asking them to log in.
This is fixed now. Guests will be returned to the forum or existing thread with a notice that their message is awaiting approval by a moderator. (Registered users whose posts are moderated can still see them.)