If you look carefully you will see that the closed toggle doesnt have rounded corners. This is because the css for the rounded corners is on btn:last-child

But the markup has a third element (hidden)

            <div class="btn-group pull-right" data-toggle="buttons-checkbox" id="filter-oc-status-div">
            <button type="button" class="btn  active btn-success " value="1">Open</button>
            <button type="button" class="btn " value="10">Closed</button>
            <input type="hidden" name="filter-oc-status" id="filter-oc-status" value="1" />
        </div>

This means that the closed button is not the :last-child