Select "arrow" hidden in bootstrap 3 input group in IE9

I have the following html styled by bootstrap 3 that defines a group of inputs:

<div class="input-group">
    <select class="form-control" >Some options here</select>
    <a class="btn btn-default input-group-addon disabled" title="Legg til" disabled="" href="#" ><i class="glyphicon glyphicon-plus-sign"></i></a>
</div>

This gives the following result in most browsers (including IE10):

However in IE9, the "arrow" for the dropdown is missing:

Anyone know a fix for this in IE9?