Combo over other control... bug ??

hi ,
putting combo over other control (group), can't select combo control.
If combo is in other position (eg 10,10) works fine, but putting "inside" group can't select combo clicking on it ??
Is this a bug or i'm doing something in wrong way

thanks in advance,
Marcelo

this is the code :
var grupo = new AW.UI.Group;
grupo.setId("grupoup");
grupo.setControlSize(520, 200);
grupo.setControlPosition(170, 100);
grupo.setControlText("Validar Usuario y Password");
document.write(grupo);

var cobj = new AW.UI.Combo;
cobj.setId("myCombo");
cobj.setControlText("some text ...");
cobj.setControlPosition(190,180);
cobj.setItemText(["Home", "Favorites", "Font size", "Search"]);
cobj.setItemCount(4);
document.write(cobj);

// look positions group in 170,170 w:520 h:200
// combo in 190,180