vote count doesn't always reflect actual votes

Its a bit contrived perhaps... but think of when you have large numbers of concurrent users. Scenario - two users vote +ve (or -ve) on the same topic within a few seconds:

Current tally of +ve votes: 10
user A clicks +: tally goes from 10 to 11
user B click +: tally goes from 10 to 11

Expected: the tally for user B should go from 10 to 12 - to reflect the actual state of voting (?)

If user B refreshes the page then it does indeed show 12, so the backed is correctly counting the votes, just not presenting the true state at the UI.