Problem with Front end select option on checkboxes

[VOI]

Hi,
when enabling the Front end select option on a checkbox element, the add button displays on the frontend as expected. When pressing the green "Add" button, i get the following Javascript error on clicking:

Uncaught TypeError: Cannot call method 'clone' of null elementlist-min.js:1
Class.startAddNewOption elementlist-min.js:1
e.extend.$owner mootools-core.js:38
(anonymous function) elementlist-min.js:1
m mootools-core.js:119

I just updated from GitHub.
Any suggestions on how to get this to work?
Thanks for your help!

 

[VOI]

Did another GitHub update today, did not change anything. If you want to take a look: http://s15402485.onlinehome-server.info/nrw/index.php/timerec/form/2/#

 

[VOI]

Works now after last GitHub update, thanks.