Yes, you didn't miss it. I had just posted the same issue to an internal forum for testers and that's where Ken's answer was coming from. The problem is that the button is supposed to occupy the whole area next to the log and it does so on other platforms but not with wxMac.
By the way, in a sense the problem also exists under Tiger. The difference is though that here, the label is not detached from the button. But as on 10.3, the button is not drawn across the whole area of the log, even though the whole area is clickable.