This will drive you nuts! (or put me to shame :-)
First, please DON'T click on the button that says "Opslaan" ("Save"). The site is already live and I'd appreciate your discretion in not messing with it.
Furthermore, you need to use a Gecko browser as I believe this is Gecko related, and the type is set to application/xhtml+xml.
Point your browser to the static page. Click on a smiley and it will insert it into the form.
Now, check out the live site (login twice with sitepoint/sitepoint) and click on a smiley. You'll see that it won't work. The debugger tells me that document.formcomment has no properties.
What the hell is going on here? The static page is just a saved version of a live page! It works on IE Win+Mac, Opera and Safari.