wax: ComboBox in Panels doesn't show up

[Norbert]

Hello List,
I try to use wax (0.2.33) to build a simple interface for a utility
script.
I want to use panels for layout, but the Combobox does not show. The
supplied examples which use Panel or GridPanel show only Button
Objects.

The following snippet demonstrates the problem:
-----
from wax import *
UMGEBUNGEN = ['prod', 'test']
class MainFrame(Frame):
def Body(self):
gp = GridPanel(self, rows=3, cols=3, hgap=1, vgap=1)
gp.AddComponent(0,0,Label(self, "Umgebung :"))
gp.AddComponent(1,1,ComboBox(self, UMGEBUNGEN, readonly=1))
gp.Pack()
self.AddComponent(gp)
# self.Pack() #uncommenting does not change anything
app = Application(MainFrame)
app.MainLoop()
-----

PythonWin 2.3.4 (#53, May 25 2004, 21:17:02) [MSC v.1200 32 bit
(Intel)] on win32.
WxPython 2.5.2.7
Am I missing something ?

Thx a lot for your time !

Norbert