Kodu şu şekilde duzenledim fakat başarılı sonuç alamadım.
<div class="form-group select-placeholder">
<label for="assigned" class="control-label">
<?php echo _l('ticket_settings_assign_to'); ?>
</label>
<select multiple name="assigned[]" id="assigned" class="form-control selectpicker" data-live-search="true" data-none-selected-text="<?php echo _l('dropdown_non_selected_tex'); ?>" data-width="100%">
<option value=""><?php echo _l('ticket_settings_none_assigned'); ?></option>
<?php foreach($staff as $member){ ?>
<option value="<?php echo $member['staffid']; ?>" <?php if($member['staffid'] == get_staff_user_id()){echo '';} ?>>
<?php echo $member['firstname'] . ' ' . $member['lastname'] ; ?>
</option>
<?php } ?>
</select>
</div>