Hello Mena,
Sorry to say, but it seems RC3 does exactly the same thing to new posts (attach them on to random old threads) on my computer anyway..... I've got an annoying cookies question to ask. Would you like me to try and post regardless, or do something else (e.g. e-mail you or Ben directly)?
Thanks in advance.
(Edit : it seems the new posts-old threads problem occurs only in some forums (particularly the General Problems forum) - I've managed to post my question in the Installation forum now - http://www.movabletype.org/support....7;t=134 Thanks.)