This is not theme bug, this is Magento bug and it's described in Magento forums. It should be fixed in next Magento release, but you can fix it manual by changing magento core file:
Open file /app/design/frontend/base/default/template/checkout/onepage/payment.phtml
Find line 36:
<fieldset><br> <?php echo $this->getChildHtml('methods') ?><br> </fieldset>
Change this code to:
<?php echo $this->getChildHtml('methods') ?><br>
Save file and upload it, now all should be fine.