So I guess this is related to
https://www.polymer-project.org/1.0/docs/devguide/events.html#annotated-listeners
I'm just a bit surprised that polymer (?) is stripping out the 'on-click' attributes when it processes the template, at least that is what I assume is happening.
Up until now it has been fairly easy to see how a web app works using just the browser dev tools, things like this will make debugging mis-behaving apps a lot more 'interesting'.