Is it possible that it takes some time before the result shows up?
I click the button: it shows the tweet window, I post the tweet.
The button shows 1.
I refresh the page: the button shows 0.
But when I try another refresh after some time, the 1 is there (don't know if someone else tweeted in the meantime, but don't think so).
You can try all the articles on my weblog if you want: http://verbaljam.nl
It's in Dutch, but 'Lees verder' means 'read more' (to come to the entry page of an article).