I recommend using this line for the Twitter code, you'll note it has the
data-url attribute the original code does not. This will force Twitter to count and link to the page via a single URL- it will not vary based on how the user is browsing the page...
Code:
<a href="http://twitter.com/share" class="twitter-share-button" data-count="horizontal" data-via="YOUR_TWITTER_USERNAME" data-url="$vboptions[bburl]/showthread.php?t=$thread[threadid]">Tweet</a><script type="text/javascript" src="http://platform.twitter.com/widgets.js"></script>