I've noticed this a few times. Sometimes when I post a message in a thread, when it should appear at the top of a new page, it's hidden and there's no link to the new page. It only appears when somebody else replies and there are two posts on that page. This has happened a few times in the past, and again just now in the Custlemm list game.

 Any ideas? Andi, do you know what might be be causing it?

That happened to me too just yesterday!  That was what fooled me into double-posting about "Wingdings encryption".

[insert standard remark about crappy CGI boards]

That happened to me on the Random Story thread a couple of months back, I posted a little note afterwards explaining why it seemed that I had double (Triple) posted, I guess I should delete that note now that I've mentioned it here...

Can we get YaBB upgraded?
http://www.yabbforum.com/downloads.php

If you do upgrade it, make sure you do a backup first!

I avoided upgrading til now because I installed so many Addons. But now I think I can go around anymore. There are just too many old bugs. A few days ago it suddenly showed all post as not read. O_o

I'll upgrad enow to an all new veresion. I hope this will help.