Most likely you are using jQuery v1.9+ and there is an issue with the buttons helper
and jQuery v1.9+ that was already reported HERE ... and it hasn't been resolved yet.
The JSFIDDLE you mention in your question is using jQuery v1.8.3 so this is why is working.
Your workaround, while the bug is fixed, is to rollback to jQuery v1.8.3.
PS. Is actually the buttons helper
js file that manages the slide show's play/autoplay option, not the thumbnail helper
;)