Vue-multiselect

Example fiddle for issue reproduction usage

HTML

<script src="https://unpkg.com/vue-multiselect@2.0.8/dist/vue-multiselect.min.js"></script>
<link rel="stylesheet" href="https://unpkg.com/vue-multiselect@2.0.8/dist/vue-multiselect.min.css">
<script src="https://code.jquery.com/jquery-3.2.1.slim.min.js"></script>
<script src="https://getbootstrap.com/docs/4.0/dist/js/bootstrap.min.js"></script>
<link rel="stylesheet" href="https://getbootstrap.com/docs/4.0/dist/css/bootstrap.min.css">
<div id="app">
<!-- Button trigger modal -->
<button type="button" class="btn btn-primary" data-toggle="modal" data-target="#exampleModal">
  Launch demo modal
</button>

<!-- Modal -->
<div class="modal fade" id="exampleModal" tabindex="-1" role="dialog" aria-labelledby="exampleModalLabel" aria-hidden="true">
  <div class="modal-dialog" role="document">
    <div class="modal-content">
      <div class="modal-header">
        <h5 class="modal-title" id="exampleModalLabel">Modal title</h5>
        <button type="button" class="close" data-dismiss="modal" aria-label="Close">
          <span aria-hidden="true">&times;</span>
        </button>
      </div>
 <!-- let's make overflow in here -->
     <div class="modal-body">
  <multiselect 
    v-model="value" 
    :options="options"
    :multiple="true"
    track-by="library"
    :custom-label="customLabel"
    >
  </multiselect>
  <br><br><br>
      </div>
      <div class="modal-footer">
        <button type="button" class="btn btn-secondary" data-dismiss="modal">Close</button>
        <button type="button" class="btn btn-primary">Save changes</button>
      </div>
    </div>
  </div>
</div>
  <pre>{{ value }}</pre>
</div>

CSS

* {
  font-family: 'Lato', 'Avenir', sans-serif;
}

.modal-body{
  overflow:auto;
  height:200px;
}

Babel + JSX

new Vue({
	components: {
  	Multiselect: window.VueMultiselect.default
	},
	data: {
  	value: { language: 'JavaScript', library: 'Vue-Multiselect' },
  	options: [
    	{	language: 'JavaScript', library: 'Vue.js' },
      { language: 'JavaScript', library: 'Vue-Multiselect' },
      { language: 'JavaScript', library: 'Vuelidate' },
      { language: 'JavaScript', library: 'Vuelidate' },
      { language: 'some', library: 'Vuelidate' },
      { language: 'more', library: 'Vuelidate' },
      { language: 'options', library: 'Vuelidate' },
      { language: 'here', library: 'Vuelidate' },
    ]
	},
  methods: {
  	customLabel (option) {
      return `${option.library} - ${option.language}`
    }
  }
}).$mount('#app')