I want to start by saying that everything was working ok last time I checked (like 2 months ago) but it seems like facebook changed something to their appi.
The URL sent back to the share form is NULL and also the count doesn't work anymore.
You can see the problem on this page.
Although still available, FB Share button was deprecated when facebook launched like button. Like button contains the sum of likes, shares and messages of URL. FB like button is easier to implement. Can you check here: https://developers.facebook.com/docs/reference/plugins/like/