Hi, I'm not sure if this has been noted before (I haven't seen any reference to it) but there's a slight bug in the submission system. If the submission is previewed then the category is reset to the first item in the list.

Around line 258 of submit.php you check for 'cid' (the category ID) via $_GET, you also need to check via $_POST so it recieves it from the preview. I just added:

if(!$cid) { $cid=intval($_POST['cid']); }

after line 258 and it now works perfectly well.

Hope this is useful .

P.S.
This is with version 2.6, just check with 2.7 on this site and the bug still seems to exist though. Line numbering may differ though.