vaadin-accordion - click listener not working?

accordion.js

<iron-form id="userForm">
<form>
  <vaadin-form-layout .responsive-steps="${this.steps}">
    <vaadin-form-item>
      <vaadin-accordion id="aclList" opened="null">
        <vaadin-accordion-panel theme="small">
          <div slot="summary">Access Control List (Advanced use only)</div>
          <div id="checkboxGroups">${this._displayAclList(this.jwt['usr']['aclList'])}</div>
        </vaadin-accordion-panel>
      </vaadin-accordion>  
    </vaadin-form-item>
  <vaadin-button theme="primary" id="userFormSubmitButton" disabled>Edit/Add User</vaadin-button>
  <vaadin-button id="userFormResetButton">Reset</vaadin-button>
  </vaadin-form-layout>
</form>
</iron-form>