Required custom_panel initialization for combo boxes (and others)

I’m working my way through building a custom for a custom component. One thing I’m curious about is required initialization. I figured out some pieces like the behaviors property but I’m stuck on using vaadin-combo-box and paper-textarea.

If I view my panel right after a reload, they don’t appear to be built by the magic in the background. If I navigate over to another panel that uses those components (like most of the developer panels) and back to my panel, they are setup and ready to go. Is there some other piece of initialization that I should be calling in my panel?

The panel code is at

I was a little confused about what was preloaded. For anyone using a custom panel that doesn’t want to deal with downloading the tools to do a rollup, if you can load another panel that initializes the components you want, you can do so with something like the following in your Polymer object declaration:

created: function() {
this.importHref(’/static/panels/ha-panel-dev-service.html’, function() {}, function() {}, true);