Uncaught NotSupportedError...

[caseybaggz]

My <paper-dropdown-meu> just recently picked up this dev tools error when you click on it to see the menu:

Not sure why? It's never done this before. Here is the code:

<paper-dropdown-menu label="Choose Your Region" style="width: 100%;">
    <paper-dropdown class="dropdown">
         <core-menu class="menu" selected="{{regionSelection}}" on-core-select="{{regionSelected}}">
             <template repeat="{{region in regionData}}">
                <paper-item name="{{region.name}}">{{region.name}}</paper-item>
             </template>
        </core-menu>
    </paper-dropdown>
</paper-dropdown-menu>