I figured out to reposition the submenu using focus & select events (as below) : http://jsfiddle.net/2zA6A/6/
$(function() {
var menuBar;
menuBar = $("#menu");
menuBar.menu(
{
focus: function (event, ui) {
menuBar.menu("option", "position", { of: $(ui.item.parent()), my: "left top", at: "right top" });
}
}
)
});