Illustrator Scripting :: Simple Dialog - Panel And Checkboxes

I have very simple dialog - just one panel and few checkboxes. When I set panel as "undefined" everything works right, but when i set a size of the panel checkboxes disappear.
 
Works
var win = new Window ("dialog", "test");
var panelOpcje = win.add("panel", undefined, "Options");
var check1 = panelOpcje.add("checkbox", undefined, "check1");
var check2 = panelOpcje.add("checkbox", undefined, "check1");
win.show();
 
This doesn't work
var win = new Window ("dialog", "test");
var panelOpcje = win.add("panel", [0,0,400,300], "Options");
var check1 = panelOpcje.add("checkbox", undefined, "check1");
var check2 = panelOpcje.add("checkbox", undefined, "check1");
win.show()