If you scan an item for renewal on circulation.pl, and the item has holds that should block renewal, you will get a message for confirmation/override. On the other hand, if you select the renewal checkbox and click the "Renew or Return checked items" button, the item will be renewed without warning.
Could be related to bug 10663.
This bug has been around for AGES. AGES. I'm not even sure how you'd go about displaying this in a properly useful way... 10 reserve boxes on a page? I think it would be better to simply remove the checkin functionality from this page.
Currently, you can not renew or return items with holds from the circulation page. Instead of the checkboxes, a link 'on hold' is displayed.