I have issue to show selected option with multiselect form, the mdb layout not showing the correct selected option as showing in standard html as I inspected.

Here is the sample code: 

<select class="mdb-select md-form" multiple>

<optgroup label="team 1">

<option value="1">Option 1</option>

<option value="2">Option 2</option>

</optgroup>

<optgroup label="team 2">

<option selected value="3">Option 3</option>

<option value="4">Option 4</option>

</optgroup>

<optgroup label="team 3">

<option value="5">Option 5</option>

<option selected value="6">Option 6</option>

</optgroup>

<optgroup label="team 4">

<option selected value="7">Option 7</option>

<option value="8">Option 8</option>

</optgroup>

</select>

<button class="btn-save btn btn-primary btn-sm">Save</button>

Here the screenshot for my inspection and its view generated.