help debug double-binding of fdicCertificateNumber as selectedBankCert on line 22

matched-bank.html

<link rel="import" href="../bower_components/polymer/polymer.html">
<link rel="import" href="../bower_components/paper-button/paper-button.html">
<link rel="import" href="shared-styles.html">
<dom-module id="matched-bank">
  <template>
    <style include="shared-styles">
    
    </style>
    <div class="matchedBank">
      <span>[[displayedBank.name]]</span>
      <span>[[displayedBank.city]], [[displayedBank.state]]</span>
      <span>[[displayedBank.fdic_certificate_number]]</span>
      <paper-button on-tap="_deliverCert">View Cost of Funds</paper-button>
    </div>
  </template>
  <script>
    Polymer({
      is: 'matched-bank',
      properties: {
        'displayedBank': Object,
        'selectedBankCert': {
          type: String,
          notify: true
        }
      },
      _deliverCert: function() {
        console.log('This log statement appears when I tap the button');
        this.selectedBankCert = this.displayedBank.fdic_certificate_number;
      }
    })
  </script>
</dom-module>

salesperson-page.html

<link rel="import" href="../bower_components/polymer/polymer.html">
<link rel="import" href="../bower_components/iron-flex-layout/iron-flex-layout.html">
<link rel="import" href="../bower_components/iron-ajax/iron-ajax.html">
<link rel="import" href="../bower_components/paper-input/paper-input.html">
<link rel="import" href="../bower_components/paper-button/paper-button.html">
<link rel="import" href="matched-bank.html">
<link rel="import" href="shared-styles.html">
<dom-module id="salesperson-page">
  <template>
    <style include="shared-styles">
      :host {
        display: block;
      }
    </style>
    <div class="card">
      <div id="bank_selection_interface">
        <paper-input id="bank_fdic_certificate_number"></paper-input>
        <paper-button on-tap="loadCert">View Bank</paper-button>
      </div>
    </div>
    <div class="card" id="bank_selector">
      <template is="dom-repeat" items="[[matchedBanks]]" selected-bank-cert="{{fdicCertificateNumber}}">
        <matched-bank displayed-bank="[[item]]">
      </template>
    </div>
    <iron-ajax
      id="bank_fetcher"
      url="http://localhost:8000/banks/fetch/[[fdicCertificateNumber]]"
      last-response="{{bank}}"
      on-response="displayBanks">
    </iron-ajax>
  </template>
  <script>
    Polymer({
      is: 'salesperson-page',
      properties: {
        bank: {
          type: Object,
          notify: true
        },
        fdicCertificateNumber: {
          type: String,
          notify: true
        },
        matchedBanks: {
          type: Array,
          notify: true
        }
      },
      listeners: {
        'fdic-certificate-number-changed': 'fetchBank'
      },
      loadCert: function() {
        this.fdicCertificateNumber = this.$.bank_fdic_certificate_number.value;
      },
      fetchBank: function() {
        console.log('However, this one does not appear');
        this.$.bank_fetcher.generateRequest();
      },
      displayBanks: function(result) {
        payload = result.detail.response;
        if (payload.banks) {
          this.matchedBanks = payload.banks;
          console.dir(this.matchedBanks);
        }
      }
    });
  </script>
</dom-module>