The Twitter button seems to not display the incorrect tweet counts. I have my Tumblr automatically share posts to Twitter. However, after I post, the Twitter button associated with that post always increments to 2. However, there should only be a single tweet. Clicking through on the button count to Twitter search confirms that the tweet count is off. You can see this on www.brickd.com.
My Tumblr code is:
Similarly, I notice the same type of behavior with the Twitter button when I was hosting a WordPress blog and a blog I have on Posterous http://www.8bitkid.com.