Well, to put it bluntly, Safari butchers the visual editor in WordPress. No idea why. Really irritating, but on a whim I fired up both Camino and Firefox to do some edits and they worked fine. Then I disabled the visual editor in my account profile and lo-and-behold Safari doesn’t end up screwing things up. So something with the visual editor and Safari is really wonky.
At least now I don’t have to cuss at this thing anymore.