Hi,
ok, i've spent some more time looking into this and discovered that the problem seems to lie within the content the client was entering in using the editor. Using content i created myself i can avoid the bug. However, when i paste their content in to your new demo editor on the site the same problem does not occur. Perhaps its a bug that got fixed in the latest version release? I've looked through their code and although a little messy i cant see any reason why it would cause this strange bug. Here is a copy of the content they created using the editor:
/forum_uploads/HTMLPage1.zip
When i paste it into the editor window as html then switch to preview i get the bug.
Perhaps my version of the cuteeditor has been corrupted somewhere along the line?