We recently switched our domain name from .be to a .com. To prevent a reset of the counter, we continue to specify the .be url on the older articles like this (we have a transparent 301 redirect from the .be to the .com urls):
<div class="addthis_toolbox addthis_default_style" addthis:url="http://thewordmagazine.be/life/back-to-zero/">
The counter then remain correct for the Google+1 and Twitter buttons, but the Facebook Like button counter is reseted. It looks like Facebook force the use of the new url, but I don't know why?
Thanks if you have any idea on this,