Yeah, have tried that (had to for a completely different reason, but handy coincidence). Also checked in a different browser (never know, sometimes helps). Have also looked, and best I can tell the code in wpdt.class.php refers to a class ui-tabs, but the css doesn’t appear to have this class, though if I’m right ui-tabs-nav would be the closest match.
And no clue at all why the buttons appear twice and don’t seem to do anything (though their not doing anything may be related to the CSS issue).