The exception: "Failed to mount: Cannot call method 'inAccordionMold' of undefined" appears when you try to build a Tabbox and its contents in two steps: the tabbox when the application runs and its content when an event happens.
See the example code here: http://zkfiddle.org/sample/16ruij2/2-Cannot-call-method-inAccordionMold-of-undefined
When the button is clicked, the exception appears. It won't happen if you change ZK version to 5.0.9.
Finally, a workaround for this is: http://zkfiddle.org/sample/16ruij2/3-Cannot-call-method-inAccordionMold-of-undefined
If the Tabpanels component is added in the first step and not in the second, the error doesn't happen.