To sync request combobox data, override the 'loader' function as:
$.fn.combobox.defaults.loader = function(param, success, error){
var opts = $(this).combobox('options');
if (!opts.url) return false;
$.ajax({
async: false,
type: opts.method,
url: opts.url,
data: param,
dataType: 'json',
success: function(data){
success(data);
},
error: function(){
error.apply(this, arguments);
}
});
};