Yeah the count issue is a widely reported problem, some people are affected some aren't, there so far doesn't seem to be a rhyme or reason to it. One option is to disable the count completely by changing "horizontal" to "none" in the code.
One thing I would try first though is this code which tells it to specifically count the URL you're twittering:
Code:
<a href="http://twitter.com/share" class="twitter-share-button" data-count="horizontal" data-via="YOUR_TWITTER_USERNAME" data-url="{vb:raw vboptions.bburl}/showthread.php?t={vb:raw threadid}" data-counturl="{vb:raw vboptions.bburl}/showthread.php?t={vb:raw threadid}">Tweet</a><script type="text/javascript" src="http://platform.twitter.com/widgets.js"></script>