Yes, when you click the vote link, Javascript bolds/unbolds it immediately, while sending a request to the server. If there's a problem with your connection, it will appear as though you've voted but when you go back the link will not be bold, since your vote will not have been received. If you don't have enough karma to downvote, the response from the server will trigger a callback which cancels the bold and informs you of your inability to downvote, assuming you have a good connection and you're still on the page.