I have looked into this further and it appears to be caused by K2 using moo tools. Javascript error is reported on page. See:

                window.addEvent('domready', function(){
                    if($('request-options')) {
                        $$('.panel')[0].setStyle('display', 'none');
                    }
                    setTask();
                });

K2 need to update for jQuery usage.

Works fine on Joomla! com_content and JEvents Menu Items.

K2 add this with the following files:

administrator/components/com_k2/elemets/category.php
administrator/components/com_k2/elemets/itemform.php
administrator/components/com_k2/elemets/k2category.php

with a script declaration.

Therefore, not a Joomla! Error.

Thanks @xtech86 for looking in this. So its not an Joomla-Error i close this Issue.