On Alex's reputation list:
A post that he down voted was deleted, hence the 1 rep it cost him to cast the vote was refunded. It's a zero change because the refund simply gave him back rep he had already earned, he didn't earn any new rep by the down vote being refunded - yet +1 was added to the value that existed while the down vote was still in place.
You saw it the way you did because:
- You don't see what he voted on, only he does and
- You don't see deleted posts in other user's profiles
A little cryptic, but the only time you see a +1 where there's no rep cap at play, it means a down vote was refunded due to being rescinded, or the post being removed.