Javafx combobox not updating dropdown size upon change on realtime? -

i using javafx v8.0.25-b18.

the problem occur size of dynamic combox's dropdown list doesn't change, if had 2 items in dropdown, dropdown size 2 items, if populate dynamic combox 3 items small scrollbar inside!?, if remove item - have blank space in combox !?

i want "reset" dropdown size each time put values it, right size each time gets populated @ runtime.

to clarify more adding 3 images:
1. first screenshot shows initial dropdown size of 2

2. the second screenshot shows same combox, @ runtime adding 2 values, expect have dropdown size of 4, instead dropdown size stays 2 , adds unwanted scrollbar

3. last screenshot when remove items , 1 item remains in combox, expect see dropdown of 1 item, instead unfortunately see dropdown size of 2 empty space instead of second item

i adding simple code create scenario, want thank @gikkman helped getting far , code his!

public class test extends application {  private int index = 0;  @override public void start(stage primarystage) throws ioexception {  vbox vbox =  new vbox(); vbox.setspacing(10); vbox.setalignment(pos.center);  final combobox<string> box = new combobox<>(); box.setprefwidth(200); box.setvisiblerowcount(10);  button add = new button("add"); button remove = new button("remove");  add.setonaction(    new eventhandler<actionevent>() {   @override   public void handle(actionevent event) {     box.getitems().add("item " + index++);     box.getitems().add("item " + index++);   } });   remove.setonaction( new eventhandler<actionevent>() {   @override   public void handle(actionevent event) {     if( index > 0 )       box.getitems().remove(--index);   } });   vbox.getchildren().addall(add, remove, box);   scene scene = new scene(vbox);  primarystage.setscene(scene); primarystage.show(); }  public static void main(string[] args) {   launch(args); } } 

try this:

box.hide(); //before set new visiblerowcount value box.setvisiblerowcount(rows); // set new visiblerowcount value box.show(); //after set new visiblerowcount value 

it's works me editable combobox , think work in case.