Probably the easiest thing for now seems to be to add the following line to your downloaded jquery-ui.css file.
.ui-tabs .ui-tabs-hide { display: none !important; }
You can put this line, by itself, as the last line in the CSS file.
This allows the 1.9 theme to work with 1.8.x
there _may_ be a 6.x release of NetTalk with an update to jQueryUI 1.9, but even if I do that not everyone will want to update, so the above instruction applies.
cheers
Bruce