The url and title given should be the one of the teaser, not the entire page.
I'm searching but reached a dead end when trying to adapt this for add this buttons.
Templates use a token [current-page:url] and in case of teaser I think [node:url] is more appropriate.
For instance, a views page of teasers with a small, but sufficient preview.
Change the issue if you don't think this is to be considered a bug.
thx in advance