You need to URL encode the # symbol with %23. This is similar to adding hash tags to the tweeted message, as discussed in this discussion on dev.twitter.com; see the reply by Ben Ward.
Only using HTML and javascript (no GWT), the following counts example.com, since the # tag is not encoded in the data-counturl property:
<a href="https://twitter.com/share" class="twitter-share-button"
data-url="http://www.example.com/#!v;id=0"
data-counturl="http://www.example.com/#!v;id=0" data-via="example">Tweet</a>
When I replace # with %23 in the data-counturl property, I get a number of 0:
<a href="https://twitter.com/share" class="twitter-share-button"
data-url="http://www.example.com/#!v;id=0"
data-counturl="http://www.exmaple.com/%23!v;id=0 data-via="example">Tweet</a>