$('#dd').flexselect(); $('#dd').change(function() { alert('never shows.'); }; <== never fires.

Quick fix:
In the pickSelected function add .change() after hidden.val().

pickSelected: function() {
  var selected = this.results[this.selectedIndex];
  if (selected) {
    this.input.val(selected.name);
    this.hidden.val(selected.value).change();  //<==
    this.picked = true;
  } else if (this.settings.allowMismatch) {
    this.hidden.val("").change();  //<==
  } else {
    this.reset();  //Maybe fire change here?
  }
}