If I try to insert a special character by clicking on the "omega" icon in the tinymce toolbar it displays the pop-up window but the character map is completely missing.

This only happens in IE9 when operating in IE9 mode. If I use the developer toolbar and tell IE9 operate in IE7 mode or IE8 mode it works as expected.

Getting out of it is a pain because the cancel button is missing when you use IE so the only way to get rid of this broken dialog was to do a refresh.