MDB Select inside modal with more than 5 options don't work.

Why mdb select in modal not working if there are more than 5 options? It just nothing happends after clicking on select. If there are 5 or less options the same select works fine.

Expected behavior Show options list after clicking on mdb-select.

Actual behavior Nothing happend

Resources (screenshots, code snippets etc.) Live example here

<!-- Button trigger modal -->
<button type="button" class="btn btn-primary" data-toggle="modal" data-target="#basicExampleModal">
Launch demo modal
</button>

<!-- Modal -->
<div class="modal fade" id="basicExampleModal" 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>
   <div class="modal-body">
    works fine:
    <select class="mdb-select md-form">
     <option value="" disabled selected>Choose your option</option>
     <option value="1">Option 1</option>
     <option value="2">Option 2</option>
     <option value="3">Option 3</option>
     <option value="4">Option 4</option>
     <option value="5">Option 5</option>
    </select>

    don't work:
    <select class="mdb-select md-form">
     <option value="" disabled selected>Choose your option</option>
     <option value="1">Option 1</option>
     <option value="2">Option 2</option>
     <option value="3">Option 3</option>
     <option value="4">Option 4</option>
     <option value="5">Option 5</option>
     <option value="6">Option 6</option>
    </select>
   </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>