I sometimes have trouble with the Thread Tools or Forum Tools not working. The box won't drop at all. I can usually solve this by navigating to another thread and then coming back. I assume it's a problem with a missing or corrupt javascript element.
You didn't say whether the Thread Tools or Search functions work properly, or if this rating issue only happens occasionally or all the time. As you can see below, all of them are in the same class of vbmenu_controls, so they ought to all behave the same way.
<td class="vbmenu_control" id="threadtools">
<a href="#goto_threadtools">Thread Tools</a>
<script type="text/javascript"> vbmenu_register("threadtools"); </script>
</td>
<td class="vbmenu_control" id="threadsearch">
<a href="#goto_threadsearch">Search this Thread</a>
<script type="text/javascript"> vbmenu_register("threadsearch"); </script>
</td>
<td class="vbmenu_control" id="threadrating">
<a href="#goto_threadrating">Rate Thread</a>
<script type="text/javascript"> vbmenu_register("threadrating"); </script>
</td>