You can see that the page reference is the /3/ marked in red above. This is using the friendly URLs extension I believe. Hope this helps as somewhere to start looking for you.
In fact, i tried to make the "whisper notification" works with a $_GET['page'] (instead of $row['name'], see : default.php line 58), to point exactly the discussion-page-comment whispered. But wasn't a good idea !! The $GLOBALS should work, but i don't know how to use it. So ... i'll wait an improvement of this add-on. Hope i'm clear.