If a reviewer comments on a diff, his/her status in the "Reviewers" section is Commented. When the diff gets updated, the icon and the status changes to Commented on a prior diff.
Similarly, when the reviewer rejects the diff and the diff gets updated, the the icon changes and the status is Rejected prior diff.
However, if he/she accepts the diff, and the diff gets updated, the icons and the status is still the same: Accepted.
That's very weird, because I would assume that changed code needs a fresh review and confirmation. Also, in the "queue" on author's Phab home page the diff is colored green, which can confuse the author and he/she can push the commit without realizing that the latest update hasn't been reviewed yet. I'm not even sure if the revision appears in the queue of reviewers who have already accepted the prior diff, or not.
Our Phab version is 20140518.git3a81f8c.