I tried your code in my machine and it worked perfectly. Perhaps your problem lies with the bootstrap combo box. So try refresh or reset the bootstrap combo box.
I have used a similar plugin and had a similar problem. So I used this and it solved my problem.
$("#select").selectpicker('refresh');
Also i found a small error in your above pasted code.
<input type= 'button' value='Add Row' id='addRow' />
instead it was like
id='addRow()'
So here is the updated code with chosen plugin.
<script type="text/javascript">
$(document).ready(function(){
$("#addRow").click(function(){
var row = "<tr>"+
"<td></td>"+
"<td><select class='chosen-select'> <option>1 --</option> <option>2 --</option> <option>3 --</option> <option>4 --</option> <option>5 --</option> <option>6 --</option> <option>7 --</option> <option>8 --</option> </select></td>"+
"<td><input style='font-size:10px;max-width:80%;' class='descInput' type='text' id='desc' name='desc' ></td>"+
"</tr>";
$("#vehReg tbody").append(row);
$(".chosen-select").chosen();
});
});
</script>
<body>
<table id='vehReg'>
<thead>
<tr>
<th>No.</th> <th>Sel</th> <th>Desc.</th>
<th ><input type= 'button' value='Add Row' id='addRow' />
<input type='hidden' value='0' id='totalRows' name='totalRows' /></th>
</tr>
</thead>
<tbody>
</tbody>
</table>
</body>
Hope this helps.
I added the code inside the javascript itself instead of the clone function. In this way it will be easier for you to maintain the count and keep adding the naming conventions to your fields.