Google Chrome latest version, Windows 7 64-bit
Create a new forum post. Press HTML button and edit with valid HTML. Press Update. Message window becomes solid empty gray block. Pressing "Post" will still post the message, but there is no way to edit or even view it after pressing Update on the HTML editor.
Note that pressing back button on browser after making the post will return to the new post page with the message window enabled and containing the message, properly formatted and editable.
Cadence you have enough trouble trying to design stable and functional PCB layout software. Please consider using one of the many mature and well-established forum systems that already exist instead of attempting to create your own, which, based on the QA I've seen, is basically doomed to fail from the start.