Switching tabs causes tab content to disappear



I have a problem with tabs switching. The content inside the tab will disappear when I switch tabs.
I’m not sure whether it is my code or a bug. I’m using 1.0.0-beta.1.

Will someone please highlight my error? My code is in here [CodePen][1]

[1]: http://codepen.io/izan/pen/Llqkp/


see fix http://codepen.io/anon/pen/ikHdj/


thanks a lot @aaronksaunders